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A  GENERAL  PHYSIOLOGY 


FOR    HIGH   SCHOOLS 


BASED  UPON  THE  NERVOUS  SYSTEM 


BY 

M.    L.    MACY,  L.B. 

ASSISTED    BY 

H.  W.  NORRIS,  A.M. 

PROFESSOR   OF   BIOLOGY,   IOWA   COLLEGE 


^^The  pJu/fiwlogy  of  the  nervous  system  is  emphalicaUy  the  physiology 
of  the  future.''  —  "MiciixEL  Foster,  M.D.,  F.R.S. 


NEW   YORK-:.  CINCINNATI  •:•  CHICAGO 

AMERICAN    BOOK    COMPANY 


Copyright,  1900,  by 
M.   L.   MACY. 

macy's  physiology. 


"^  PREFACE 


The  effort  has  been  made  in  this  book  to  unify  the  study  of  the 
parts  and  the  functions  of  the  human  organism  by  the  application  of 
approved  pedagogical  and  scientific  principles.  The  teaching  of  any 
science  proceeds  logically  from  that  which  is  known  to  that  which  is 
not  known.  Physiology  is  one  of  the  earliest  of  the  natural  sciences 
to  be  presented  for  formal  study  in  school.  In  respect  to  man's 
organism  the  one  sort  of  knowledge  absolutely  original  and  elemental 
is  consciousness^  —  conscious  motion  and  sensation.  This  it  is  that 
forms  the  most  apparent  difference  between  the  two  kingdoms  which 
manifest  the  phenomena  of  life.  It  is  characteristic  of  animals  to 
possess  consciousness,  volition,  feeling.  Plants  are,  to  all  appearance, 
devoid  of  them  all. 

Hence  this  study  of  human  physiology  is  made  to  begin  with  that 
part  of  the  body  which  is  the  organ  of  consciousness  —  the  nervous 
system.  The  pupil  knows  that  he  thinks  and  feels  and  wills  and 
moves,  and  he  studies  physiology  in  order  to  understand  the  appara- 
tus by  which  these  wonders  are  accomplished.  He  is  here  given  first 
(after  a  few  preliminary  definitions)  a  brief  sketch  of  the  parts  com- 
posing the  nervous  system.  Next  he  studies  those  physical  operations 
into  which  consciousness  enters  as  an  essential  quality,  and  becomes 
familiar  with  the  organs  of  motion  and  sensation.  This  leads  natu- 
rally to  consideration  of  the  provision  for  the  sustenance  of  those 
organs  —  nutrition  in  its  comprehensive  sense.  Finally  the  student 
comes  to  a  more  detailed  examination  of  the  mechanism  for  the 
conscious  activities  of  the  human  being. 

Whatever  may  be  true  of  philosophers,  the  infant  begins  the  study 
of  physiology  at  the  point  here  suggested,  and  follows  a  method  in 
harmony  with  this  plan.  More  than  one  practical  teacher  has  worked 
out  a  similar  method  through  years  of  experience  in  the  class  room. 
By  making  the  nervous  system  (the  center  and  core  of  all  animal 
life)  the  leading  thought  throughout,  a  unity  of  impression  is  secured, 

3 


4  PEEFACE 

the  actual  connection  of  every  vital  process  with  the  one  nervous 
system  becomes  obvious,  and  the  emphasis  is  placed  where  it  properly 
belongs.  It  is  believed  that  this  plan  has  advantages  also  for  the 
student  of  general  biology.  It  emphasizes  the  one  grand,  obvious 
distinction  between  plants  and  animals.  To  students  of  psychology 
it  will  likewise  commend  itself.  Because  of  prevalent  ignorance  of 
the  nervous  system  and  its  due  predominance  in  the  animal  economy, 
psychologists  have  been  forced  to  become  physiologists  in  order  to 
build  across  the  gap,  left  by  the  ordinary  manner  of  treatment, 
between  physiology  and  psychology. 

Care  has  been  taken  to  make  no  statements  not  in  accord  with 
established  science,  but  no  eifort  is  made  to  introduce  the  newest 
conjectures.  The  necessary  limitations  of  a  school  text-book  have 
been  kept  in  mind  as  well  as  the  degree  of  mental  development  of 
those  for  whom  the  work  is  designed. 

It  is  believed  that  the  instruction  respecting  alcoholic  drinks  and 
narcotics,  while  complying  with  the  requirements  of  i-ecent  legislation 
in  the  various  states,  will  be  found  to  be  based  upon  rational  and 
scientific  principles,  and  to  be  placed  before  the  student  in  a  manner 
to  win  the  assent  of  his  reason  rather  than  to  create  a  mere  prejudice 
which  further  knowledge  might  overthrow.  Nothing  is  gained  by 
overstatement,  and  it  is  always  safe  to  tell  the  simple  truth,  for 
nothing  will  so  surely  foster  right  living  as  a  knowledge  of  the  truth. 

The  writer  has  had  much  assistance  from  experienced  and  compe- 
tent-teachers and  physicians.  Dr.  A.  W.  Alvord  (M.D.,  University 
of  Michigan)  of  Battle  Creek,  Michigan,  has  kindly  revised  the 
hygienic  portions  of  the  book.  Mr.  H.  W.  Xorris,  A.  M.,  Professor  of 
Biology  in  Iowa  College,  has  read  and  criticised  the  whole  of  the 
manuscript.  All  of  the  experimental  work  has  been  prepared  by  him 
and  will  be  found  of  especial  value.  Many  of  the  illustrations  used 
are  such  as  are  commonly  found  in  schoolbooks  treating  the  subject 
of  physiology,  but  a  large  number  have  been  adapted  from  cuts  in 
recent  advanced  works,  mainly  those  by  Morris,  Spalteholz,  and  A^an 
Gehuchten;  while  numerous  other  drawings  expressly  for  this  work 
have  been  made  Ijy  Mr.  E.  AV.  Atherton  under  the  direction  of 
Professor  Norris. 


CONTENTS 


PART   I 


CHAPTER 
I. 

ir. 
III. 


INTRODUCTION 


Matter  and  Cells  .... 

Tissues  and  Organs      .... 
A  General  View  of  the  Nervous  System 


19 

27 


PAET   II 


CONSCIOUS   NERVOUS   OPERATIONS 
SENSATION 


MOTION  AND 


IV.  The  Eramework  of  the  Body,  or  the  Osseous  Sy 

V.  The  ^luscular  System  .... 

VI.  The  Skm  as  an  Organ  of  Sensation  —  Touch 

VII.  Taste  and  Smell 

VIII.  The  Eye  and  the  Sense  of.  Sight  . 

IX.  The  Ear  and  the  Sense  of  Hearing 

X.  The  Vocal  Apparatus  .         .         .        . 


stem 


37 

59 

82 

94 

101 

126 

136 


PART   III 


NERVOUS   OPERATIONS   UNCONNECTED   WITH 

CONSCIOUSNESS 


XI.  Blood.  Lymph,  and  Chyle  . 

XII.  The  Circulatory  System 

XIII.  Nervous  Control  of  the  Circulation 

XIV.  Respiration  ..... 
XV.  Nervous  Control  of  the  Respiratory  Apparatus 


147 
153 
176 

181 
198 


6  CONTENTS 

CHAPTER  PAGE 

XVI.  Food 201 

XVII.  The  Digestive  Apparatus  and  Nutrition      ....  218 

XVIII.  Tlie  Ductless  Glands 254 

XIX.  The  Organs  of  Excretion .  257 

XX.  The  Heat  of  the  Body 266 


PART   IV 

THE  NEKVOUS   SYSTEM 

XXI.     Anatomical  Description 275 

XXII.     Functions  of  the  Nervous  System 297 

XXIII.     Hygiene  of  tire  Nervous  System 314 


PAET  V 

THE   PRESERVATION  OF  HEALTH 

XXIV.     Health  and  Disease 335 

XXV.     Common  Accidents  and  Injuries 344 

XXVI.     Public  Hygiene,  or  General  Sanitation        ....  360 

Glossary 369 

Index 395 


PART  I 

INTRODUCTION 

It  is  customary  to  divide  the  study  of  the  human  body 
into  three  departments:  (1)  Aiiatomy^  which  is  the  science 
that  describes  the  structure  of  the  body;  (2)  Physiology^ 
or  the  science  of  the  functions,  or  uses,  of  the  various 
parts  of  the  body,  and  (3)  Hygiene^  or  the  science  of 
health,  which  treats  of  the  care  of  the  body  and  all  its 
parts  for  the  purpose  of  maintaining  the  whole  in  its  best 
condition  for  usefulness  and  enjoyment.  The  term  Physi- 
ology^ as  applied  to  a  schoolbook,  however,  is  often  used 
to  include  all  three  of  these  lines  of  study. 


Fig.  1. — The  nervous  system. 


CHAPTER   I 

MATTER  AND   CELLS 

1.  Living  and  Lifeless  Matter.  — What  matter  is  we  are 
not  yet  able  to  say,  but  as  it  exists  in  our  world  it  may  be 
separated  into  two  great  divisions,  —  living  matter  and 
lifeless  matter.  So  far  as  present  knowledge  goes,  these 
two  sorts  of  matter  are  Avholly  distinct  the  one  from  the 
other,  and  lifeless  matter  never  becomes  living  matter 
except  under  the  influence  of  matter  already  living.  The 
same  substances  are  indeed  found  in  the  two  sorts  of 
matter,  and  when  living  matter  is  killed,  or  becomes  life- 
less, no  change  can  be  discovered  in  its  weight.  That 
mysterious  something  called  life  is  therefore  not  material, 
and  living  matter  may  be  said  to  be  only  ordinary  lifeless 
matter  existing  in  a  different  state  or  condition. 

2.  Chemical  Elements.  —  A  substance  which  cannot  be 
divided  into  two  or  more  different  kinds  of  matter  is 
called  a  chemical  element  or  a  simple  substance.  All 
others  are  called  compound  substances.  Matter  is  sepa- 
rated into  its  elements  by  processes  which  affect  the  mole- 
cules or  the  atoms  of  which  it  is  composed,  that  is,  by 
chemical  analysis. 

A  molecule  may  be  defined  as  the  smallest  particle  of 
matter  which  exists  alone  and  retains  most  of  the  proper- 
ties of  the  mass  of  the  substance.  An  atom  is  one  of  the 
ultimate  particles  of  which  a  molecule  is  composed.     The 

9 


10  INTRODUCTION 

molecules  of  chemical  elements  are  composed  of  atoms  of 
the  same  kind.  Compound  substances  have  atoms  of  dif- 
ferent kinds.  There  are  as  many  kinds  of  atoms  as  of 
elements.  Both  atoms  and  molecules  are  too  small  to  be 
seen  even  with  powerful  microscopes. 

A  drop  of  water  may  be  divided  mechanically  into 
many  small  j^ortions,  and  each  part  will  retain  all  the 
characteristics  of  the  original  drop.  But  when  the  chem- 
ist separates  the  oxygen  and  hydrogen  which  together 
make  wp  the  drop  of  water,  he  has  no  longer  any  matter 
which  resembles  water,  but  instead  two  kinds  of  gaseous 
matter  of  entirely  different  properties.  The  water  has 
been  resolved  by  chemical  analysis  into  its  chemical 
elements. 

Chemical  elements  unite  in  different  proportions  with 
one  another  to  form  a  great  variety  of  substances. 
About  seventy-five  elements  have  been  isolated  by  chem- 
ists, but  only  a  few  of  them  are  known  to  enter  int©  the 
structure  of  animal  bodies.  These  are  carbon,  oxygen, 
hydrogen,  nitrogen,  sulphur,  phosphorus,  chlorine,  fluorine, 
silicon,  potassium,  sodium,  lithium,  calcium,  magnesium, 
iron,  and  manganese.  As  a  rule  these  elements  exist  in 
the  body  in  some  sort  of  combination  with  one  another. 

3.  Protoplasm  is  a  name  given  to  living  matter.  It  is 
a  clear,  jelly  like  substance  containing  minute  grains. 
As  protoplasm,  it  cannot  be  chemically  analyzed,  because 
the  process  of  analysis  destroys  its  vitality  so  that  it  is  no 
longer  protoplasm,  but  merely  dead,  lifeless  matter.  The 
one  essential  thing  about  protoplasm  is  that  it  is  alive ; 
dead  protoplasm  is  a  contradiction  in  terms.  It  has  been 
called  "  the  physical  basis  of  life,''  because  without  it  life 
does  not  exist,  and  witli  it  there  is  always  life.  But  the 
material  of  winch  protoplasm  is  composed  is  found,  when 


MATTER    AND   CELLS  11 

analyzed  after  it  has  ceased  to  live,  to  be  highly  complex. 
A  largo  part  of  its  weight  is  ivater,  while  its  solid  portion 
is  chieily  composed  of  lyroteids.  These  are  substances 
found  ill  many  foods,  white  of  Qgg  being  a  familiar  example. 
They  contain  carbon,  hydrogen,  oxygen,  and  nitrogen. 

4.  The  Cell  (Fig.  2).— All  living  bodies,  both  plants 
and  animals,  are  found  to  consist  of  cells.  Cells  are 
the  ultimate  units  of  which  living  be- 
ings are  made  up,  just  as  bricks  are 
the  units  of  which  a  brick  wall  is  com- 
posed. A  cell  is  a  microscopic  bit  of 
protoplasm,  Avith  or  without  an  inclos- 
ing wall,  having  suspended  Avithin  it  a 

rounded  body  of  denser  material  called  Fig.  2.  — Diagram  of 
■  T  ^  T.  IT-  .  tJie  parts  of  a  ceU. 

the  nucleus.     It  may  be  living  apart,  or 

p  r  xi  -^        £  ^'  nucleus. 

may  lorm  one  or  the  units  oi  an  organ-  &  cell  body  or  proto- 
ism.     Plant  cells  have  usually  the  cell  ?J^^^^^: 

wall,  but  an  animal  cell  may  be  only  a 
naked  speck  of  living  matter.     Free  cells  tend  to  assume 
a  round  shape,  but  under  pressure  they  may  take  almost 
any  form. 

5.  The  cells  of  the  human  body  vary  in  size  from  g^^- 
to  3-0V0  ^^  ^^^  inch  in  diameter.  All  animals  begin  their 
existence  as  single  cells,  and  the  life  of  any  animal  is  the 
sum  of  the  activities  of  all  its  separate  cells,  while  its 
physical  structure  consists  of  the  cells  themselves  and  the 
intercellular  matter  which  they  produce,  together  with 
the  various  lifeless  substances  which  they  deposit  within 
themselves. 

6.  Essential  Properties  of  Cells. — All  living  things  pos- 
sess two  properties  without  which  they  cannot  exist. 

One  of  these  properties  is  mitrition,  —  using  the  word  in 
its  broader  sense  to  include  the  double  process  of  taking 


12  INTRODUCTION 

in  material  from  outside  and  building  it  into  the  bodily 
structure,  —  that  is,  the  making  of  complex  chemical  com- 
pounds out  of  simpler  ones ;  and  the  breaking  down,  or 
reducing  to  simpler  forms,  of  compounds  already  formed. 
The  former  results  in  growth  or  repair  of  cell  substance, 
and  is  the  storing  up  of  energy ;  the  latter  is  the  setting 
free  of  energy,  and  the  production  of  waste  material  to  be 
removed  as  no  longer  valuable.  Nutrition  includes  all 
the  chemical  changes  which  take  place  in  living  matter. 

The  other  essential  property  of  living  bodies  is  the 
power  of  7'eproduction^  or  of  giving  rise  in  some  way  to 
living  beings  like  themselves. 

The  first  of  these  properties,  nutrition,  belongs  to  every 
individual  cell,  to  every  plant,  and  every  animal,  as  neces- 
sary to  its  own  continued  existence.  The  second,  repro- 
duction, is  needful  only  for  the  continued  existence  of  the 
race,  and  is  in  some  cases  possessed  only  by  certain  indi- 
viduals of  the  race.  Single  cells  are,  however,  capaBle  of 
giving  rise  by  self-division  to  other  cells  like  themselves. 

Life  is  sustained  by  the  ceaseless  exercise  of  the  two 
powers  of  nutrition  and  reproduction. 

7.  Other  Properties  of  Living  Cells.  —  Certain  other 
properties  are  found  to  exist  in  most  cells  in  the  body, 
for  example,  in  the  white  corpuscles  of  human  blood, 
which  are  clearly  defined  nucleated  cells. 

These  are  contractility^  or  instability,  that  is,  the  power 
of  changing  form  without  the  application  of  pressure ; 
irritability^  or  the  power  of  vigorous  action  under  stimulus, 
as,  for  instance,  when  the  blood  cells  contract  under  the 
influence  of  electricity  ;  conductivity^  or  the  power  of  pass- 
ing on  to  distant  parts  of  the  cell  the  influence  exerted 
by  a  stimulus  upon  a  single  point ;  and  coordination^  or 
the  capacity  in  all  the  parts  to  work  together  in  definite 


MATTER   AND   CELLS  13 

direction  and  with  regulated  strength  to  accomplish  an 
end,  as  when  a  particle  of  material  suitable  for  building 
up  a  cell  is  drawn  in  and  used  for  that  purpose. 

8.  Plants  and  Animals.  — Xo  naturalist  can  at  the  pres- 
ent day  place  his  finger  upon  a  line  of  separation  and 
say:  All  living  things  upon  this  side  are  plants;  all  upon 
that  side,  animals.  It  is,  indeed,  easy  to  distinguish  the 
higher  forms  of  animal  life  from  the  higher  forms  of  plant 
life,  and  the  most  striking  difference  is  that  the  animal 
possesses  the  power  of  spontaneous  movement,  while  the 
plant  is  rooted  to  one  spot.  Other  distinctions  appear  as 
the  two  forms  of  life  are  studied.  For  example,  both  are 
dependent  for  their  continued  life  and  growth  upon  the 
food  which  is  supplied  from  without  themselves ;  but 
plants  (with  few  exceptions)  subsist  solely  upon  carbon 
dioxide,  water,  and  mineral  salts,  while  animals  live  upon 
water  and  those  chemical  compounds  Avhich  have  formed 
part  of  living  bodies,  that  is,  organic  materials.  Ani- 
mals cannot  use  mineral  substances  as  food  except  as  they 
are  mixed  with  organic  matter.  But  the  simj^lest  forms 
of  plant  and  animal  life  cannot  be  distinguished  with 
positiveness  from  each  other.  Both  consist  of  single  pro- 
toplasmic cells,  and  it  is  not  possible  to  show  that  the  proto- 
plasm of  one  is  essentially  different  from  that  of  the  other. 

As  animals  rise  in  the  scale  of  being,  however,  they  are 
found  to  develop,  as  plants  do  not,  a  nervous  system  of 
ever-increasing  complexity  and  importance.  Hence  man, 
as  an  animal,  may  be  said  to  be  distinguished  from  all 
other  animals  by  the  superiority  of  his  nervous  system  ; 
and  all  tlie  other  parts  of  the  human  body  may  be  consid- 
ered as  created  simply  to  minister  in  some  way  to  that 
superior  portion  of  the  human  frame  which  is  the  direct 
agent  or  instrument  of  the  highest  manifestations  of  life. 


14  I^^TKODlTCTION 

9.  The  Difference  between  Plants  and  Animals  in  Respect 
to  Stimulus.  —  Living  animal  cells  possess  the  property  of 
irritabilit}^  or  excitability,  that  is,  some  change  in  their 
composition  results  from  the  action  of  stimulus.  Vegeta- 
ble cells  also  possess  this  property  in  some  degree.  But  it 
is  found  that,  as  in  the  processes  of  development  more  and 
more  complex  forms  of  plant  life  appear,  the  plant  does 
not  develop  special  organs  for  the  transmission  of  stimulus. 
In  the  animal  kingdom,  on  the  other  hand,  a  striking  dif- 
ference appears.  In  one  of  the  lowest  known  representa- 
tives of  animal  life — the  amoeba  (Fig.  3,  p.  16),  which 
is  a  mere  microscopic  lump  of  naked  protoplasm  —  each 
minute  particle  of  the  protoplasm  appears  to  respond  to 
a  stimulus  and  to  transmit  it  to  the  adjacent  particles, 
there  being  no  distinction  of  parts  or  functions  in  the 
single  cell.  But  in  the  next  higher  division  of  ani- 
mals, the  corals,  sea  anemones,  etc.,  the  rudiments  of  a 
nervous  system  are  visible,  and  some  division  of •  sense 
organs  appears.  It  is  probable  that  nervous  impressions 
are  received  first  in  but  a  single  form,  while  a  gradual 
and  uninterrupted  development  of  the  senses  follows  as 
we  rise  in  the  scale.  That  is,  one  of  the  lower  animals 
may  be  said  to  have  but  one  sense,  touch,  or  a  general  sen- 
sibility, —  it  receives  but  one  kind  of  sense  impression 
from  influences  Avhich  higher  animals  recognize  as  diverse, 
—  while  higher  animals  may  distinguish  two  or  more  kinds 
of  impression,  and  so  on.  It  should  be  noticed  that  the 
common  division  of  senses  into  touch,  taste,  smell,  sight, 
and  hearing  is  somewhat  arbitrary,  even  man  not  being 
always  able  to  discriminate,  for  instance,  between  taste 
and  smell,  Avhile  certain  sensations  are  recognized,  such 
as  perception  of  temperature  and  of  pain,  which  do  not 
strictly  belong  to  any  of  the  "  five  senses  "  so  called. 


matter  and  cells  15 

Suggestions  kegakding   the  Practical  Work 

The  amount  of  illustrative  experimental  work  in  physi- 
ology that  can  be  done  in  a  high  school  depends  chiefly 
upon  two  factors :  the  material  equipment  of  the  school 
and  the  tact  of  the  teacher. 

Vivisection  doubtless  has  its  place,  but  not  in  the  pub- 
lic schools.  Ordinary  dissections  sensibly  performed  can 
be  made  a  successful  part  of  class  work  in  most  of  our 
high  schools,  but  occasionally  deference  to  public  opinion 
will  require  that  the  dissections  be  performed  only  by  the 
teacher,  or  possibly  not  at  all. 

No  attempt  is  made  in  this  book  to  give  detailed  direc- 
tions for  dissecting,  nor  for  the  preparation  of  material 
for  study  with  the  compound  microscope.  It  is  assumed 
that  a  teacher  of  advanced  physiology  has  received  some 
preliminary  training  in  anatomy  and  microscopical  meth- 
ods. If  so,  then  suggestions  will  be  far  better  than  spe- 
cific directions. 

It  is  not  expected  that  all  the  experiments  will  be  per- 
formed by  a  class.  When  a  compound  microscope  is  not 
available,  some  of  the  exercises  must  necessarily  be  omit- 
ted. It  is  believed,  however,  that  all  the  demonstrations, 
dissections,  and  experiments  can  be  performed  in  any 
school  of  moderate  equipment.  A  great  mistake  is  made 
when  much  apparatus  is  interposed  between  the  student 
of  elementary  science  and  the  objects  of  his  study.  The 
teacher  should  make  sure  that  the  illustration  is  not  sub- 
stituted for  the  idea  that  it  is  intended  to  explain.  In 
some  instances  conditions  will  require  that  the  teacher 
perform  most  of  the  work  of  an  experiment,  but  as  far 
as  possible  the  pupil  should  himself  be  responsible  for 
each  detail. 


16 


INTRODUCTION 


Fig.  3. 


Amoeba  in  eight  successive  stages 
of  movement. 


Demonstrations  and  Experiments  i 

1.  Ainceha.  —  The  amoeba  is  not  always  easily  obtained.  If  debris 
of  water  plants  be  kept  in  shallow  dishes  of  water  for  several  days, 
there  can  nsually  be  found  specimens  of  amoeba  in  the  scnm  that 

forms  on  the  surface  of 
the  water,  or  in  the 
ooze  that  collects  at  the 
edges  and  bottoms  of 
the  dishes.  On  mount- 
ing some  of  the  material 
on  a  glass  slide  and  ex- 
amining with  the  com- 
pound microscope,  there 
may  be  seen  small,  irreg- 
ular, transparent  masses 
of  a  jellylike  nature 
moving  along  very  slowly  with  a  rolling  or  flowing  motion  (Fig.  3). 
Attention  should  be  given  to  the  constantly  changing  form  of  the 
animal,  which  thus  exhibits  a  fundamental  characteristic  of  proto- 
plasm, instability.  If,  when  an  amoeba  is  fully  extended,  sendjng  out 
processes,  pseudopodia,  from  the  main  part  of  the  body,  the  slide  be 
gently  tapped,  the  animal  will  be  seen  to  contract  quickly  into  a 
rounded  mass,  showing  another  characteristic  of  protoplasm,  irritability, 
or  the  capacity  of  response  to  stimulus. 

2.  White  Blood  Corpuscles.  —  If  a  drop  of  fresh  human  blood,  or 
preferably  of  frog's  blood,  be  mount- 
ed on  a  glass  slide  and  examined 
with  the  compound  microscope, 
among  the  numerous  red  corpuscles 
may  be  seen  a  few  transparent  ones 
(Fig.  4).  On  remaining  undisturbed 
for  some  time  they  change  in  shape,  -p^^  4. -Blood  cells  (corpuscles) 
or  even  migrate,  in  a  manner  similar  of  frog. 


1  Note  to  Teachers.  —  The  demonstrations  and  experiments  should 
precede  the  recitation  of  the  lessons  which  they  illustrate.  The  pupil 
should  not  be  required  to  describe  the  brain,  for  example,  until  he  has 
studied  the  dissected  organ  itself. 


MATTER   AND   CELLS 


IT 


Fig.  5.  — Compound  microscope  with  sim- 
ple warming  stage  (IF)  attached. 


to  that  of  the  amoeba.     Fresh  blood  may  be  obtained  by  pricking  the 

finger  with  a  sterilized  needle,  and  by  decapitating  or  pithing  a  frog. 
3.    Movements  of  Protoplasm 

in  Plants.  —  The  phenomena 

of    protoplasmic    movements 

can  be  observed  in  a  variety 

of   i^lants.     The    Stoneworts, 

Chara   and   Nitella,  and   the 

stamen   hairs  of  the   Spider- 
wort,     Tradescantia,    furnish 

some  of   the    best  examples. 

In  all  these  the  protoplasm  is 

inclosed  in  a  cell  wall,   and 

when  observed  with  the  com- 
pound microscope  is  seen  to 

exhibit  streaming  movements 

and  circulation  of  particles  in 

the  contents  of  the  cell.    The 

response    of     protoplasm    to 

changes  in   temperature  can 

be  very  easily  shown  by  placing  the  slide  on  a  warming  stage  upon 

the  microscope  stand  as  shown  in  Fig.  5.  When  the  warming  stage 
is  heated,  the  protoj^lasmic  movements  are  seen  to 
increase  in  ra^Didity  up  to  a  certain  point.  As  it 
cools,  the  movements  become  slower. 

4.  Properties  of  Protoplasm  in  Muscle.  —  In  some 
animals  the  various  tissues  retain  their  vitality  and 
properties  for  a  considerable  time  after  the  death 
of  the  individual  animal.  The  common  frog  fur- 
nishes us  one  of  the  best  examples  of  this.  If  a 
frog's  gastrocnemius  muscle  with  sciatic  nerve  at- 
tachments (Fig.  6)  be  dissected  out  (see  Figs.  7 
and  8)  shortly  after  decapitation  of  the  animal,  it 
w^ll  retain  its  properties  for  a  considerable  length 
of  time,  if  kept  well  moistened  with  normal  salt 
solution  (0.75  per  cent  solution  of  common  salt).- 
If  the  nerve  be  cut  w^ith  sharp  scissors  a  contrac- 
tion of  the  muscle  occurs.  Touching  the  nerve 
with  a  red-hot  needle  produces  a  similar  contraction 


Fig.  6.  —  Nerve- 
muscle  prepara- 
tion. 

F  femur. 

G  gastrocnemius 

muscle. 
iS    sciatic  nerve. 
T  tendon      {tendo 

Achilles) . 


MACY'S    PHYS. 


2 


18 


INTRODUCTION 


in  the  muscle.  Placing  the  fresh-cut  end  of  the  nerve  in  a  saturated 
solution  of  connnon  salt  brhigs  about  a  series  of  coutractions  in  the 
muscle.    The  muscle  also  contracts  when  the  nerve  is  stimulated  with 

a  weak  electric  cur- 
rent. If  the  nerve 
muscle  preparation 
be  placed  on  a  copper 
plate,  and  the  tem- 
perature of  the  latter 
be  raised  above  or 
lowered  below  the 
normal,  there  will  oc- 
cur variations  in  the 
response  of  the  mus- 
cle to  stimuli.  (Elec- 
trical stimulation  will 
be  found  most  con- 
venient.) The  rela- 
tion of  muscular 
action  to  temperature 
will  thus  be  striking- 
ly represented.  These 
experiments  with  the 
nerve-muscle  prepa- 
ration show  that  the 
living  substance  is 
irritahle,  unstahle,  and 
conductive  of  stimuli. 
5.  Cells.  — The 
amoeba  and  the  white 
blood  corpuscles  al- 
ready studied  furnish 
very  good  examples 
of  cells  which  liave  no  fixed  form  nor  definite  shapes.  The  red  blood 
corpuscles  of  the  frog  are  cells  in  which  the  nucleus  can  be  easily  dis- 
cerned by  aid  of  the  microscope  (Fig.  4,  p.  16). 


Muscles  of  the  left  leg  of  the  frog.    Fig.  8  shows 
distribution  of  the  sciatic  nerve. 


ad  M.  adductor  magnus 
h     M.  biceps. 
y     M.  gastrocnemius. 
p     M.  pyriformis. 
pe  M.  iieroneus. 


sc    sciatic  nerve. 
sm  M.  semimembranosus. 
St    M.  semitendinosus. 
ta    M.  tibialis  anticus. 
ti'    M.  triceps. 


ri    M.  rectus  internus  minor 


CHAPTER    II 

TISSUES  AND  ORGANS 

10.  The  human  body,  beginning  as  a  single  cell,  is 
gradnally  built  up  by  a  process  of  division  and  subdivision 
of  that  cell,  so  that  the  complete,  adult  man  is  but  a 
mass  of  cells  with  some  cementive  and  connective  matter. 
It  is  found,  hoAvever,  that  differences  early  appear  in  the 
characteristics  of  different  cells,  and  these  differences 
increase  as  development  proceeds.  A  group  of  similar 
cells  having  a  similar  function  is  called  a  tissue. 

11.  Differentiation  of  Tissues.  —  In  the  lowest  animals, 
composed  of  but  a  single  cell,  all  the  dift'erent  parts  of 
the  body  are  essentially  alike  (leaving  the  nucleus  out  of 
consideration)  and  have  the  same  functions.  One  part 
may  move  as  well  as  another.  All  parts  share  in  the 
process  of  nutrition,  and  one  part  responds  as  well  as 
another  to  stimulus.  But  the  higher  animals  are  found 
to  be  made  up  of  unlike  parts,  which  minister  in  dift'er- 
ent  ways  to  the  life  of  the  whole  being.  As  the  cells 
multiply,  certain  groups  of  cells  become  changed  in 
such  a  manner  as  to  adapt  them  to  the  performance 
of  some  special  function,  while  other  parts  are  adapted 
to  other  functions.  A  number  of  cells  lying  together 
become  modified  so  as  to  make  up  a  tissue  adapted  to 
a  certain  purpose.  Other  cells  become  modified  in  a 
dift'erent   way   to    form    a   tissue   adapted   to    a   different 

19 


20  INTRODUCTION 

purpose,  and  the  whole  body  becomes  a  mass  of  many 
different  tissues,  each  having  its  definite  and  special  char- 
acteristics and  structure.  This  process  is  known  as  dif- 
ferentiation of  the  tissues,  and  is  accompanied  by  what  is 
called  physiological  division  of  labor.  One  tissue  is  better 
adapted  to  the  performance  of  a  certain  office  in  the  body 
than  are  others,  and  that  special' work  is  given  it  to  do,  so 
that  the  work  of  carrying  on  the  operations  of  the  body  is 
divided  up  among  the  tissues. 

12.  Organs.  —  A  living  being  is  often  called  an  organism. 
In  order  to  secure  the  greatest  efficiency  in  their  labors, 
the  various  tissues  are  built  up  into  a  multitude  of  mecha- 
nisms called  organs;  for  example,  the  eye,  the  hand,  the 
liver.  Several  different  kinds  of  tissue  often  enter  into 
the  structure  of  a  single  organ,  and  the  same  sort  of  tissue 
appears  in  many  different  organs. 

A  number  of  organs  so  arranged  and  related  to  one 
another  as  to  cooperate  in  carrying  on  a  special  process 
or  series  of  processes,  is  called  a  system,  —  as  the  diges- 
tive system,  or  the  nervous  system. 

13.  Classification  of  Tissues.  —  Tissues  are  variously  clas- 
sified by  different  authors,  but  one  broad  distinction  may 
be   noted  which   divides   them   into   two   great   classes : 

(1)  The  tissues  which  have  to  do  with  the  setting  free  of 
energy.      These    are   the  muscular  and  nervous  tissues. 

(2)  The  tissues  wliich  have  to  do  with  renewing  the  sub- 
stances and  restoring  the  power  of  responding  to  stimulus. 
In  this  second  class  are  grouped  all  the  remaining  parts 
of  the  body,  Avhich  include  tissues  differing  widely  from 
one  another  —  from  the  solid,  hong  tissue  of  the  skeleton, 
and  the  still  harder  enamel  which  covers  the  teeth,  to  the 
soft  substance  composing  the  brain,  the  elastic  fat  which 
rounds  out  the  figure,  and  the  fluid  which  we  call  blood. 


TISSUES  AND   ORGANS  21 

14.    The  following  table  shows  this  classification  :  — 


1.  Tissues  which  have  to  do  with  liberating  j  Muscular 
energy  —  Master  Tissues  1  Nervous 


Tissues  which 
have  to  do 
with  the  pro- 
tection, sup- 
port, and 
renewal  of 
the  Master 
Tissues 


^  a.  Pavement 

b.   Cubical, 

Sphe- 

Snnple Epi- 

roidal, 

thelium 

and  Co- 

Epithelial 

lumnar 

Tissues 

Compound 

c.  Ciliated         ^  , 

r  Columnar 

Transitional       Ciliated 

Epithe-      . 
Hum 

Stratified        '    Squamous 
[      or  Scaly 

■  Areolar 

a.  White 

Fibrous 

b.  Yellow 

Connective 

Adipose 

or  Elas- 

Tissues    ' 

Cartilage 
Bone 
.  Blood 

tic 

15.  The  Master  Tissues.  —  Muscular  tissue  liberates 
energy  which  takes  the  form  of  motion  attended  by  some 
measure  of  heat.  But  the  changes  in  muscular  tissue 
by  which  energy  is  liberated  are  guided,  regulated,  and 
adapted  to  the  purposes  of  human  life  by  means  of  nervous 
tissue;  that  is,  the  muscles  are  the  instrument,  but  an 
instrument  motionless  and  useless  until  the  nerves  supply 
the  impulse  which  sets  the  muscles  at  work.  A  muscle 
develops  energy  under  the  action  of  nervous  stimulus  con- 
veyed to  the  muscle  cell  through  nervous  tissue.  Energy 
is  set  free  in  nervous  tissue  when  the  nervous  organ 
is  stimulated  by  the  influence  adapted  to  it.  The  nerves 
carry  the  impulse  to  the  muscle,  and  energy  is  liber- 
ated as  motion  and  heat.  Muscular  and  nervous  tissues 
possess  irritability^  that  is,  they  respond  to  stiinulus,  in 


22 


INTRODUCTION 


the  one  case  by  contraction,  in  the  other  by  some 
change  not  yet  understood,  giving  rise  to  what  is  called  a 
"  nervous  impulse,"  and  in  the  act  they  develop  energy 
by  the  breaking  down  of  their  own  substance.  Unless 
that  substance  is  renewed  the  tissue  will  cease  to  respond  to 
stimulus,  —  will  die.  The  remaining  tissues  of  the  body, 
therefore,  are  engaged  in  one  way  or  another  in  preparing 
the  needful  food,  in  conveying  it  to  these  "  master  tissues," 
in  taking  up  the  waste  substances  produced  in  the  evolu- 
tion of  energy  and  preparing  them  for  removal  from  the 
body,  or  in  furnishing  mechanical  support  to  the  body  and 
its  various  parts.  In  these  processes  are  involved  all  the 
parts  which  are  concerned  in  digestion,  respiration,  circu- 
lation, and  excretion.  This  varied  and  complex  series  of 
operations  implies  a  vast  array  of  muscular  movements, 
and  all  are  governed  by  the  nervous  system  under  the 
action  of  its  varied  stimuli. 

16.  Epithelial  Tissues.  —  The  free  surfaces  of  thef  body, 
both  within  and  without,  are  covered  with  a  tissue  called 
epithelium.       Simple  epithelium   is  composed    of    but    one 

layer  of  cells,  ar- 
ranged like  flat  pav- 
ing stones  and  fitted 
together  with  a  very 
little  cementing  mate- 
rial (Fig.  9,  A).  The 
epithelium  of  this  va- 
riety found  lining  the 
interior  of  the  blood 
vessels,  and  some  other  surfaces  which  are  not  exposed 
to  the  outer  air,  is  called  endothelium. 

The  cubical^  spheroidal.,  and  columnar  epithelial  tissues 
are   named  from    the   shape  of    tlieir  cells.      In   ciliated 


Fig.  9  —Columnar  epithelmm. 
A  simple.        B  stratified. 


TISSUES   AND   ORGANS 


23 


epithelium  each  of  the  cells  is  surmounted 
b}'  tapering,  hairlike  filaments  (Fig.  10). 

Compound  epithelium  is  composed  of  more 
than  one  layer  of  cells  (Fig.  11).  Epithe- 
lium contains  no  blood  vessels,  but  is  nour- 
ished by  lymph.  It  forms  the  external  layer 
of  the  skin  and  the  mucous  membrane. 

17.  Connective  Tissues  exist  in  many  diverse 
forms,  but  all  are  alike  in  origin,  being  devel- 
oped from  the  same  layer  of  the  embryo ; 
alike  in  structure,  haying  a  large  amount 
of  intercellular  material ;  and  alike  in  func- 
tion, being  devoted  to  supporting  and  connecting  the 
master  tissues. 


Fig.  10.  — Cili- 
ated epithe- 
lium from  a 
small  bron- 
chial tube. 


A  B 

Fig.  1 1 .— Compound  stratified  epithelium. 

A  vertical  section  of  the  skin.  B  lateral  view  of  the  cells. 

C  flat  side  of  scales  like  d,  magnilied  250  diameters,  showing  the  nucleated 
cells  transformed  into  broad  scales. 

Areolar  tissue  is  made  up  of  cells,  wliite  and  yellow 
fibers,  and  some  intercellular  matter  (Fig.  12).  It  is 
found  widely  distributed  through  the  body,  appearing  as 
delicate,  elastic,  sheathing  membrane  for  muscles,  nerves, 
glands,  and  other  organs.  It  penetrates  into  the  sub- 
stance of  the  organs  and  connects  and  supports  their 
various  parts. 


24 


INTRODUCTION 


White  fibrous  tissue  is  found  in  ligaments  and  tendons, 
the  tough  lining  membranes  of  bones,  brain,  etc.  (Fig.  13, 
A).  It  is  composed  mainly  of  bundles  of  strong,  white 
fibers  containing  nucleated  cells. 


Bundle  of  White  Fibers 

Fig.  12— Diagram  of  areolar 

tissue. 


A  ■  HI  B 

Fig.  13.  — Fibrous  tissue. 

A  white  fibrous  tissue.  • 

B  elastic  or  yellow  fibrous  tissue. 


Elastic  or  yelloiv  fibrous  tissue  contains  yellow,  elastic 
fibers  (Fig.  13,  B)  bound  into  bundles  by  areolar  tissue. 
It  appears  in  some  ligaments,  and  in  the  walls  of  the 
arteries,  and  in  the  air  cells  of  the  lungs. 

Adipose  tissue  is  the  fat  of  the  body,  and  is  found  in 
nearly  all  parts,  usually  in  connection  with  areolar  tissue. 
Adipose  tissue  consists  of  protoplasmic  cell  walls  filled 
with  liquid  fat. 

18.  Cartilage  appears  in  two  forms,  —  hyaline  cartilage 
(Fig.  14;  \\m\  fihrocartilafje  (Fig.  15),  the  first  being  clear 
and  free  from  fibers,  the  second  composed  largely  of  white 
or  yelh)w  fillers.  Cells  are  found  in  all  kinds  of  cartilage, 
but  tliere  is  always  a  proportionately  large  amount  of  inter- 
celbilar  matter  wliich  is  produced  l)y  the  cells. 


TISSUES   AND   ORGANS 


25 


mm 


Fig.  14.  —  Hyaline  cartilage. 

a   group  of  four  cartilage  cells, 
c  a  cell.  71   nucleus. 

77?   matrix. 


Fig.  15.  — Fibrocartilage. 

c  cartilage  cells  surrounded  by- 
hyaline  matrix  (7??). 
/  fibrous  tissue. 


19.  Bone  is  more  solid  than  the  other  tissues.  It  is 
penetrated  throughout  by  minute  canals,  called  Haver- 
sian canals,  containing  blood  vessels  (Fig.  16).     The  final 


/  ^rte^  -^-^-^^^-  ^^-^'-^ 


\'>  h 


*^  W  ^:^P^''^%^^s 


Fig.  16.      Cross  section  of  bone. 

a  lacunae,  spaces  in  living  bone  occupied  by  bone  cells. 
b  Haversian  caual. 


26 


INTRODUCTION 


structure  of  bone  is  fibrous,  and  along  with  the  fibers  are 
cells  called  hone  corpuscles^  while  the  cementing  material 
^  is   earthy   matter.     In    many  situa- 

tions, parts  which  are  in  early  life 
composed  of  cartilage  become  after- 
ward replaced  by  bone,  through  the 
process  called  ossification. 

20.  Blood  is  a  fluid  connective  tis- 
sue which  conveys  nutriment  to  all 
parts  of  the  body  (Fig.  17).  It 
holds  suspended  in  its  liquid  por- 
tion, or  plasma^  large  numbers  of 
cells  called  corpuscles.  These  are 
of  two  sorts,  named  from  their  color  the  red  or  colored 
corpuscles,  and  the  white  or  colorless  corpuscles.  The 
latter  have  one  or  more  nuclei,  while  the  red  corj)uscles 
have  none. 


Fig.  17.  — Human  blood 
corpuscles. 

R  red.         W  white. 


CHAPTER    III 

A  GENERAL  VIEW   OF   THE   NERVOUS   SYSTEM 

21.  The  great  clistinguishiiig  feature  separating  man 
as  an  animal  from  all  other  animals  is,  as  we  have  seen, 
his  possession  of  a  nervous  system  of  more  complex  and 
intricate  structure  than  any  other  in  the  animal  kingdom. 
It  is  now  fully  recognized  that  the  nervous  system  is  the 
central,  unifying,  coordinating  element  in  the  human 
organism  —  that  for  which  all  other  parts  exist  and  to 
which  all  are  subordinate.  In  order,  therefore,  to  under- 
stand clearly  the  part  which  each  portion  of  the  body  is 
designed  to  play  in  the  general  plan,  it  is  necessary  to 
have  some  general  knowledge  of  the  nervous  system, 
while  a  fuller  study  of  its  parts  and  their  functions  may 
be  postponed  to  a  later  period. 

22.  Divisions  of  the  Nervous  System.  —  Physiologists  have 
been  accustomed  to  describe  two  great  divisions  of  the 
nervous  system,  called  the  central  or  cerehro-spiiial  sys- 
tem^ and  the  ganglionic  or  sympathetic  system^  the  first 
having  control  of  sensation  and  voluntary  motion,  the 
second  presiding  over  those  vital  operations  not  under 
voluntary  control,  its  nerves  being  in  general  distributed 
to  the  internal  organs  and  the  blood  vessels.  It  has, 
however,  long  been  understood  that  there  are  not  two 
nervous  systems,  but  one.  Still,  as  a  matter  of  conven- 
ience in  description,  the  well-known  terms  are  generally 

27 


28 


INTRODUCTIOK 


Si 


retained,    and    the    nervous   system    is 
treated  under  its  twofold  aspect. 

23.  The  Cerebro-spinal  System  is  com- 
posed of  the  brain  and  the  spinal  cord, 
with  the  nerves  passing  from  them  to 
the  various  parts  of  the  body  (see  Fig. 
1,  p.  8,  and  Fig.  18). 

24.  The  Brain  fills  the  cavity  of  the 
skull.  It  consists  of  five  principal 
parts  :  (1)  the  cerebrum ;  (2)  the  ojjtic 
thalamic  which  are  so  closely  united  to 
the  cerebrum  as  to  seem  to  be  a  part  of 
it ;  (3)  the  optic  lobes^  or  corpora  quad- 
rigemina^  and  crura  cerebri;  (4)  the 
cerebellum^  and  with  it  the  pons  Varolii  ; 
(5)  the  medulla  oblongata  (Figs.  19  and 
20).  Looked  at  from  above  or  from 
the  side,  the  only  parts  of  the«brain 
that  appear  are  the  cerebrum,  a  part 
of  the  cerebellum,  and  part  of  the 
medulla  oblongata. 

25.  Cranial  Nerves. — From  the  un- 
der surface  of  the  brain  arise  twelve 
pairs  of  nerves  (Fig.  19),  which  pass 
through  openings  in  the  cranial  bojies 
and  are  distributed  in  a  manner  to  be 
described  hereafter.  They  are  of  three 
classes  :  (1)  Nerves  of  special  sensa- 
tion ;  (2)  motor  nerves,  that  is,  nerves 
which  carry  nervous  impulses  to  the 
muscles   and  cause   them   to   contract; 

Fig.  18,  -Brain  and    and  (3)  mixed  nerves,  that  is,  both  sen- 
spinal  cord,  ventral  , 
(anterior;  view.           ^'^H  ^nd  motor. 


A  GENERAL    VIEW   OE   THE   NERVOUS   SYSTEM 


29 


Olfactory  Bulb 

l^to  u'hich  is  attached 
the  Olfactory  Nerve) 

Pituitary  Body _^ 

Optic  Xe  rve~  ~ 

Optic  Chiasma 

Oculomotor  Nerve — _ 

Trochlear  Nerve — 

Trigeminal  Nerve — 

Pons  Varolii--. 

Abducens  Nerve- - 

Facial  Nerve-— 

Auditory  Nerve- ^ 

Glossopharyngeal  Nerve  -_ 

Vagus  Nerve 1 

Spinal  accessory  Nerve — 
Hypoglossal  Nerve — 

Medulla  Oblongata 

First  Spinal  Nerve 

Cerebellum — 

Spinal  Cord — 

Second  Spinal  Nerve — 


Fig.  19. 


Ventral  (anterior)  surface  of  the  brain. 


26.  The  Spinal  Cord  and  Spinal  Nerves.  —  The  spinal 
cord  is  a  column  of  soft  nervous  matter,  filling  the  long 
channel  in  the  spinal  col- 
umn (Fig.  18).  Thirty- 
one  pairs  of  nerves  arise 
from  the  spinal  cord, 
each  having  two  roots, 
—  a  posterior  and  an 
anterior  root  (Fig.  21). 
Upon  the  posterior  root, 
just  before  it  unites  with 
the  anterior  root,  is  a 
little  knot  of  nervous 
matter    called   a    spinal 


Fig.  20.— Side  view  of  brain. 

a  cerebrum,     h  cerebellum, 
c  medulla  oblongata. 


30 


INTRODUCTION 


Fig.  21.  — Diagram  of  cross  sec- 
tion of  spinal  cord,  showing 
nerve  roots. 

P  posterior  root  of  spinal  nerve. 
G  ganglion.    A  anterior  root. 
S   spinal  nerve. 


ganglion.  The  anterior  roots  of  spinal  nerves  contain 
what  are  called  efferent  nerve  fibers,  that  is,  fibers  carry- 
ing impulses /rom  the  nerve  center.  These  are  sometimes 
called  motor  nerve  fibers,  because  their  stimulation  usually 

results  in  motion ;  but  the 
term  is  not  strictly  accurate, 
since  other  than  motor  im- 
pulses may  pass  over  efferent 
nerves.  Posterior  roots  con- 
tain afferent  nerve  fibers,  that 
is,  fibers  carrying  impulses 
toward  the  nerve  center.  They 
are  also  called  sensory  nerve 
fibers,  because  when  they  are 
stimulated  feeling  or  sensation  most  often  results,  but  other 
impulses  than  sensory  ones  may  be  conveyed  by  them. 

27.  The  Sympathetic  System  consists  of  a  chain  of  ganglia 
lying  on  each  side  and  in  front  of  the  spinal  column,  of 
three  jwdln  plexuses  (or  nerve  networks)  in  the  cavities  of 
the  chest  and  abdomen,  of  many  small  ganglia  in  all  parts 
of  the  body,  and  of  an  immense  number  of  fine  nerve  fibers 
(Fig.  22).  Each  ganglion  of  the  chain  is  connected  by 
nerve  fibers  with  the  one  above  and  the  one  below,  as  well 
as  with  the  spinal  cord.  In  general,  the  number  of  pairs 
of  ganglia  corresponds  to  the  number  of  vertebrse,  or  seg- 
ments of  the  backbone;  but  there  are  only  three  pairs  of 
ganglia  in  the  neck,  and  in  front  of  the  coccyx,  or  last 
segment  of  the  backbone,  there  is  only  a  single  ganglion. 

28.  Gray  and  White  Nervous  Matter. — Two  kinds  of 
nervous  matter,  easily  distinguished  by  their  color,  are 
found  in  the  body.  In  the  cerebrum  and  the  cerebellum 
the  gray  matter  is  mainly  in  the  surface  layer,  called  the 
cortex^  the  deeper  portions  being  of  white  matter  ;  while  in 


Cervical  Spin 
Nerves 


Dorsal  Spinal  , 
Nerves        \ 


Lumbar  Spinal 
Nerves 


Fig.  22. —Diagram  of  the  sympathetic  nervous  system. 

G  ganglion  chain.  Co  coccygeal  spinal  nerve. 

31 


32 


INTRODUCTION 


the  spinal  cord  the  reverse  is  tlie  case,  a  central  column  of 
gray  matter  being  surrounded  by  white  matter  (Figs.  23 

and  24). 
The  gan- 
glia are 
composed  ^^ 

a  1  m  O  S  t  Fig.  24.  —  Cross  sec- 
whollyof    tion  of  spinal  cord, 
•^  snowing    arrange- 

graymat-    ment  of  gray  and 
I  white  matter. 

29.  Nerve  Cells.  —  Gray 

nervous   matter   is  made 

_.    „.     _  ^.       -*r,  V     •    -u        up  mainlv  of    nerve  cells 

Fig.  23.— Cross  section  of  the  hemispheres     ^  -^ 

of  the  brain,  showing  arrangement  of  (Fig.    25).       These    vary 

gray  and  white  matter.  ^^^^^^j^    .^^  ^.^^   ^^^^^  ^^^^p^^ 

Each  sends  out  one  or  more  branches,  or  processes,  one 
of  which  forms  the  central  core  of  a  nerve  fiber  and 
is  called  the  axis  cylinder  process.  A  ganglion  is. a  col- 
lection of  nerve  cells  imbedded  in  nerve  fibers. 

30.    Nerve  Fibers.  —  Every  nerve  fiber  has  connection 
with  at  least  one  nerve  cell,  for  its  central  strand,  called 

the  axis  cylinder.,  is  al- 
ways the  axis  cylinder 
process  of  a  nerve  cell 
(Fig.  26).  This  is  the 
essential,  indispensable 
part  of  the  nerve  fiber. 
Surrounding  the  axis  cyl- 
inder there  is  usually  a 
layer  of  white,  oily  mat- 
ter called  the  medullary 
sheath,  and  outside  of 
that  is  a  thin  inclosing  membrane  called  the  neurilemma. 


Fig.  25. 


Nerve  cells  (mitral)  from  the 
olfactory  bulb. 


A   GENERAL   VIEW   OF   THE    NERVOUS   SYSTEM 


33 


The  last  is  continuous  for  the  whole  length  of  the  fiber, 
but  the  medullary  sheath  is  broken  at  short  intervals  by 
little  spaces  called  nodes.  Some  fibers 
have  only  the  neurilemma,  and  are  there- 
fore gray  in  color  ;  for  it  is  the  medullary 
sheath  which  gives  the  characteristic  shin- 
ing white  appearance  to  nerves  and  nerve 
fibers.  Those  fibers  possessing  the  sheath 
are  called  meduUated  nerve  fibers;  those 
without  it  are  called   nonmedullated. 


Demonstrations 


Node  of 
)    Ranvier 


Neurilemma 


Neuraxon 
or  Axis 
Cylinder 


Medullai 
'Sheath 


Fig.  26.  — Por- 
tion of  a  me- 
duUated nerve 
fiber. 


6.  The  Brain.  —  The  brain  of  the  sheep  will  be 
found  to  be  very  satisfactory  in  demonstrating  to  a 
class  the  general  structure  of  this  portion  of  the  cen- 
tral nervous  system.  The  brain  of  the  cat,  dog,  or 
ox  may  be  used  instead.  The  brain  can  be  removed 
from  the  skull  by  sawing  away  the  roof  of  the  latter 
and  with  a  scalpel  cutting  the  attaching  membranes 
and  nerves.  The  brain  should  be  prepared  some 
days,  or  even  weeks,  before  it  is  needed  by  the  class, 
and  hardened  and  preserved  in  some  suitable  me- 
dium. Strong  alcohol,  a  2  to  5  per  cent  solution  of 
formalin  (formol)  in  water,  and  a  2  to  5  per  cent 
solution  of  bichromate  of  potash  are  very  good  hard- 
ening and  preserving  reagents.  But  more  satisfactory  is  the  following 
mixture  :  95  per  cent  alcohol,  six  parts  ;  2  per  cent  solution  of  formalin, 
four  parts.  When  specimens  are  preserved  in  a  fluid  containing  for- 
malin, they  should  be  soaked  in  water  a  short  time  before  using,  to 
avoid  the  irritating  effects  of  formalin  vapor  on  the  eyes,  etc.  AVhere 
possible,  each  student  should  be  provided  with  one  of  the  preserved 
specimens.  A  brain  recently  removed  should  be  at  hand,  but  it  will 
be  found  to  be  too  soft  for  much  careful  study.  With  care  one  pre- 
served brain  may  be  made  to  suffice  for  an  entire  class.  After  exami- 
nation the  specimens  may  be  preserved  for  more  detailed  study  later 
on.  In  studying  the  brain  follow  the  descriptions  of  the  general  text. 
macy's  phys.  — 3 


34  INTRODUCTION 

7.  The  Spinal  Cord. — Procure  at  a  slaughterhouse  a  spinal  cord  of 
an  ox  and  examine  it  fresh,  or  preserve  it  in  one  of  the  fluids  men- 
tioned in  the  preceding  section.  Preserved  portions  can  be  used  later 
in  a  more  careful  study  of  the  structure  of  the  cord. 

8.  The  Sympathetic  Nercous  System.  —  If  the  abdominal  cavity  of  a 
dog,  cat,  rat,  or  frog  be  opened  and  the  viscera  displaced,  there  maybe 
seen  on  each  side  of  the  backbone  a  v^hite  cord  with  grayish  enlarge- 
ments, ganglia.  The  two  cords  and  their  ganglia  constitute  the  main 
chains  of  the  sympathetic  system. 

9.  Nerve  Fibers.  —  Tease  out  with  needles  in  water  on  a  glass  slide 
a  small  piece  of  a  nerve.  Even  without  the  aid  of  a  lens  the  nerve  is 
seen  to  be  composed  of  small,  threadlike  fibers.  Examined  with  the 
compound  microscope  the  fibrous  structure  will  become  more  apparent. 


PART  II 

CONSCIOUS   NERVOUS    0PP:RAT10NS;    MOTION 
AND    SENSATION 

Of  many  of  the  processes  which  have  to  do  with  man's 
life  he  is  wholly  or  partly  unconscious.  The  wonderful 
operations  of  growth  and  development  go  on  chiefly  with- 
out his  knowledge.  The  nerve  cells  which  order  and 
direct  all  the  vital  activities  carry  on  their  work  so  silently, 
so  regularly,  so  skillfully  —  without  jar  or  confusion  — 
that  neighboring  cells  may  not  even  know  that  they  are 
busy. 

Of  other  nervous  activities  a  man  is  fully  conscious,  and 
without  his  consciousness  the  object  of  those  operations 
is  not  accomplished.  A  large  part  of  the  nervous  system 
and  a  large  part  of  the  other  tissues  and  organs  of  the 
body  have  for  their  chief  business  the  production  of  con- 
scious motio7i.  Other  sets  of  nerves,  nerve  cells,  and 
special  organs  are  employed  in  bringing  about  those 
experiences  called  sensations.  These  two  objects  are 
effected  through  what  may  be  called  conscious  nervous 
operations :  motion  being  the  result  of  the  action  of  cer- 
tain nervous  impulses  upon  bones  and  muscles  ;  sensation^ 
the  result  of  the  action  of  other  nervous  impulses  upon 
the  special  organs  for  sensation. 

In  order  to  understand  these  conscious  nervous  opera- 
tions it  is  necessary  to  study  the  skeleton  and  joints,  the 
muscular  system,  the  skin  as  a  sense  organ,  the  senses 
of  taste,  smell,  sight,  and  hearing,  and  the  apparatus  for 
speech. 

35 


PECTORAL   GIRDLE 


Fig.  27.  — The  skeleton. 
36 


CHAPTER  IV 

THE  FRAMEWORK  OF  THE  BODY,  OR  THE  OSSEOUS  SYSTEM 

31.  Functions  of  the  Bones.  —  Certain  parts  of  an  animal 
bod}^  are  more  essential  to  its  existence  than  others,  and 
more  important  to  its  well-being.  These  portions  are  of 
especial  delicacy  in  substance  and  structure,  and  pecul- 
iarly liable  to  injury.  They  therefore  require  protection. 
For  this  purpose  the  more  solid  substances  which  make  up 
the  body  are  arranged  to  inclose  or  shield  the  softer  and 
more  delicate  parts. 

In  one  large  group  of  animal  forms,  called  invertebrates, 
which  includes  insects,  mollusks,  crabs,  lobsters,  etc.,  the 
outer  portion  of  the  body  consists  usually  of  a  more  or 
less  hard  and  tough  crust  called  the  exoskeleton,  which 
covers  the  softer  parts.  But  the  higher  group  of  animals, 
called  vertebrates  or  backboned  animals,  to  which  man 
belongs,  possess  an  inner,  bony  framework,  called  the  e7i- 
doskeletoru  so  arranged  as  to  form  a  support  and  a  defense 
to  the  more  sensitive  and  more  essential  parts. 

In  all  vertebrates  the  skeleton  consists  of  a  somewhat 
firm  but  flexible  bony  column  to  which  are  attached  the 
bones  of  the  head,  the  ribs,  and  the  pectoral  and  pelvic 
girdles,  which  connect  respectively  the  upper  and  the 
lower  limbs  with  the  trunk  (Fig.  27). 

The  bones  of  tlie  skeleton  furnish  the  necessary  levers 
and  points  of  support  for  tlie  muscles  which  are  the  organs 
of  motion. 

37 


38  CONSCIOUS   NERVOUS   OPERATIONS 

32.  Provision  for  Movement  in  Different  Classes  of  Ani- 
mals.—  A  distinguishing  feature  of  the  animal  kingdom 
is*  the  power  of  voluntary  motion,  and  the  ability  at  some 
period  of  life  to  move  about  from  place  to  place.  For  this 
purpose  the  different  classes  and  orders  of  animals  are 
provided  with  a  great  variety  of  mechanical  devices. 
Certain  aquatic  creatures  propel  themselves  by  means  of 
pulsations  in  the  whole  body.  Snakes  and  worms  swim 
by  the  undulations  of  the  body.  The  squid  fills  a  certain 
cavity  within  itself  with  water  and  then  suddenly  expels 
it,  and  the  force  of  the  ejection  moves  the  body  in  one 
direction  or  another,  according  to  the  direction  of  the 
current  of  water  ejected.  The  jellyfish  propels  itself 
by  drawing  in  and  expelling  water  from  its  bell-shaped 
body.  Animalcules  move  themselves  by  the  rapid  vibra- 
tions of  innumerable  hairlike  projections.  But  all  the 
higher  forms  of  animals  move  by  means  of  muscles  and 
ligaments  attached  to  an  internal  solid  framework,  or 
skeleton. 

33.  The  Vertebrate  Skeleton.  —  A  careful  study  of  any 
vertebrate  skeleton  discloses  marvelous  adaptations  for 
accomplishing  the  two  main  objects  of  protection  and 
motion.  Protection  to  the  vital  parts  might  have  been 
secured  by  means  of  a  rigid,  unyielding  case,  but  in  order 
to  allow  motion  in  all  parts  of  the  body  also,  the  skele- 
ton is  composed  of  many  separate  pieces  united  together 
by  elastic  tissues.  The  whole  number  of  bones  in  the 
adult  man  is  about  206,  while  in  the  child  the  number  is 
yet  larger,  because,  as  a  child  grows  older,  certain  bones 
which  are  at  first  distinct  (and  remain  so  in  the  lower  ani- 
mals) grow  together  to  form  one.  For  convenience  in 
study,  the  bony  framework  is  divided  into  two  parts  called 
the  axial  skeleton  and  tlie  appeyulicular  skeleton. 


THE   FRAMEWORK    OF   THE    BODY 


39 


34.  Axial  Skeleton.  —  The  bones  of  the  head,  neck,  and 
trunk  compose  the  axial  skeleto7i. 

35.  The  Skull.  —  At  the  upper  extremity  of  the  vertebral 
column  appears  the  skull  (Fig.  28),  composed  of  (I)  the 
cranium^  the  strong 

casket  which  in- 
closes the  most  pre- 
cious part  of  the 
animal  structure,  — 
the  brain  —  and  (2) 
the  various  bones 
forming  the  skeleton 
of  the  face. 

36.  The  Cranium. 
—  In  the  adult  the 
cranium  consists  of 
eight  bones,  each 
composed  of  two 
firm,  compact  plates 
with  a  spongy  layer 
between.  The  bones 
which  form  the  arch 
of  the  head  are 
closely  joined  to- 
gether by  irregu- 
larly notched  edges, 
the  lines  of  union 
being  called  sutures. 

The  cranial  bones  are  named  as  follows:  1.  The  fron- 
tal bone,  forming  the  front  of  the  skull  and  of  especial  solid- 
ity and  thickness,  as  most  exposed  to  injury.  2.  The 
parietal  bones,  a  pair  of  thin,  flat  bones  meeting  along  the 
top  of  the  head.     3.    The  temporal  bones,  below  the  parietal 


Fig.  28.— The  skull. 


1  frontal  bone. 

2  parietal  bone. 

3  temporal  bone. 

4  sphenoid  bone. 

5  ethmoid  bone. 

10  nasal  bone. 

11  inferior  maxillary  (lower  jaw)  bone 


6  occipital  bone. 

7  superior    maxillary 
(upper  jaw)  bone. 

8  malar  bone. 

9  lachrymal  bone. 


40  CONSCIOUS   NERVOUS   OPERATIONS 

on  each  side,  and  having  large  openings  leading  into  the 
ear  cavities.  4.  The  sphenoid,  forming  part  of  the  floor 
of  the  brain  cavity.  5.  The  ethmoid^  forming  part  of 
the  floor  in  front  and  joined  to  many  of  the  facial  bones. 
It  is  perforated  for  the  passage  of  the  olfactory  nerves. 
6.  Th.Q  occqntal,  a  large  bone  at  the  back  of  the  head  and 
also  a  part  of  the  floor  of  the  sknll.  It  is  perforated  by 
small  holes  through  which  pass  nerves,  and  b}^  a  large 
opening  called  the  foramen  magnum  for  the  passage  of  the 
spinal  cord  to  its  union  with  the  brain. 

37.  The  Facial  Skeleton  consists  of  fourteen  bones:  7.  The 
superior  maxillary  hones,  or  upper  jaw  bones,  carrying 
the  upper  teeth  and  forming  most  of  the  hard  palate. 
8.  The  malar  hones,  or  cheek  bones.  9.  The  lachrymal 
hones,  near  the  inner  angle  of  the  socket  of  the  eye,  and  per- 
forated for  the  tear  ducts.  10.  The  nasal  hones,  forming 
the  roof  of  the  nose.  11.  The  inferior  maxillary  or  lower 
jaAV  bone.  12.  The  inferior  turhinate  hones,  one  ifl  each 
nostril  chamber.  13.  The  vomer,  forming  part  of  the  par- 
tition between  the  nostrils.  14.  The  palate  hones,  Avhicli 
complete  the  skeleton  of  the  hard  palate. 

38.  The  Hyoid. —  A  small  U-shaped  bone  secured  by 
long  ligaments  to  the  base  of  the  skull  and  lying  in  the 
neck  at  the  root  of  the  tongue,  is  called  the  hyoid  hone 
(Figs.  79,  80,  and  82,  pp.  136,  138).  It  furnishes  points 
of  attachment  for  many  muscles. 

39.  Bones  of  the  Ear.  —  Three  minute  bones  in  the  middle 
ear  (Figs.  74  and  75),  the  malleus,  the  incus,  and  the  stapes, 
have  to  do  witli  the  conduction  of  sound. 

40.  The  Vertebral  Column.  —  In  a  man  of  average  stature 
the  spinal  column  is  about  twenty-eight  inches  in  length. 
It  consists  of  twenty-six  separate  bones  (Fig.  29).  The 
upper   part,  wdiich   includes  more    than   half    the   whole 


THE   FRAMP]WORK   OF   THE    BODY 


41 


length  of  the  column, 
IS  made  up  of  twenty- 
four  separate  bones, 
each  called  a  vertebra. 

Of  these  the  first 
or  upper  seven  lie  in 
the  neck  and  are 
called  cervical  verte- 
hrce. 

The  next  twelve 
bones  of  the  spinal 
column  are  those  to 
which  the  ribs  are 
attached.  They  are 
called  the  tJwracie  or 
dorsal  vertehrce. 

Next  come  the  lum- 
bar vertebrce,  which 
are  larger  than  any 
other  of  the  movable 
vertebrae.  They  sup- 
port no  ribs,  but  re- 
ceive many  large  and 
strong  muscles. 

Below  these  is  seen 
the  sacrum,  composed 
in  the  infant  of  five 
vertebrcT,  Avhich  in 
the  adult  become  one 
bone.  To  the  broad 
spaces  on  its  sides  are 
attached  the  bones  of 
the  pelvic  arch  which 


Fig.  29.— The  vertebral    column    as    seen 
from  left  side  (.1)  and  from  behind  (/>'). 

C  1-7,  J)  1-12,  L  1-5  cei-vical,  dorsal,  and  lum- 
bar vertebriB. 
S    sacrum.  sp  spinous  process. 

Co  coccyx,  tr  transverse  process. 


42 


CONSCIOUS   NERVOUS   OPERATIONS 


supports  the  lower  limbs.     It  has  eight  openings,  which 

communicate  with  the  canal  inclosing  the  spinal  cord  and 

permit  the  passage  of  spinal  nerves. 

At  the  lower  end  of  the  spinal  column  is  the  coccyx, 

formed  by  the  union  of  four  very  small  vertebrae  into  one 

bone.     It  is  that  part  of  the  skeleton  which  in  the  lower 

vertebrate  animals  forms  the  tail. 

41.   The  Vertebrae   vary  somewhat  in  form,  but   are   all 

constructed  upon  the  same  general  plan  (Fig.  30).  There 
is  a  stout  bony  cylinder,  called  the 
hody^  or  centrum.  To  this  solid  cen- 
trum is  attached  an  arch,  called  the 
neural  arch^  which  forms,  with  the 
back  of  the  centrum,  an  inclosed 
space  named  the  neural  ring.  The 
successive  neural  rings  form  in  the 
spinal  column  a  long  tube  in  which 
the  spinal  cord  may  safely  lie. 

From  the  back  of  the  neural  arch 
extends     a    long    bony    projection 


called  the 


Fig.  30.  — A  dorsal  verte- 
bra shown  in  two  posi- 
tions. 

1  centrum.        2  processes. 
3  neural  ring. 


spinous  process^ 


and  the 


successive  processes,  or  spines  (Fig. 

29),  extending  down  the  backbone, 

give  to  it  the  name  of  spinal  column. 

Six  other  processes  project  from 
each  vertebra:  one  on  each  side  called  transverse  pro- 
cesses;  two  called  anterior  articular  processes^  extending 
forward ;  and  two  called  posterior  articular  processes^ 
extending  backward,  to  meet  the  corresponding  processes 
of  the  neighboring  vertebrae.  These  processes  form,  by 
means  of  the  intervening  cushion  of  cartilage  and  con- 
necting ligaments,  a  joint  permitting  a  slight  amount  of 
motion. 


THE   FRAMEWORK   OF   THE    BODY 


43 


Two  shallow  depressions  in  the  forward  portion  of  the 
Centrum  of  each  of  the  dorsal  vertebra),  with  correspond- 
ing depressions  in  the  adjoining  vertebra,  form  pits  which 
receive  the  heads  of  the  ribs.  Similar  depressions  at  the 
ends  of  the  transverse  processes  of  the  dorsal  vertebne 
assist  in  securing  the  ribs  to  the  spine  (Fig.  31). 


Fig.  31.  — Articulation  of  a  pair  of  ribs  to  a  vertebra. 


ce  centrum  of  the  vertebra. 
tr  transverse  process. 

St  sternum. 


r    rib. 

CO  costal  cartilage. 


Between  each  two  adjoining  vertebrae  are  elastic  cush- 
ions of  fihrocartilage,  which  assist  in  providing  for  motion 
and  flexibility  in  the  spinal  column  and  in  preventing 
injurious  jarring  of  the  brain  and  spinal  cord. 

42.  The  Atlas  and  Axis.  — The  first  two  cervical  vertebrae 
have  certain  modifications  of  structure  for  the  sake  of 
the  freer  motion  needful  in  the  neck.     The  atlas  or  iirst 


44 


CONSCIOUS  NEKVOUS   OPERATIONS 


vertebra  (Fig.  32,  A)  supports  the  skull,  being  articulated 
by  two  shallow  hollows  (a,  h)  with  corresponding  pro- 
jections on  the  occipital  bone  above.  This  permits  the 
head  to  rock  back  and  forth.  The  atlas  has  a  very  small 
body  or  centrum,  and  a  large  neural  ring  subdivided  by 
the  transverse  ligament.  Into  the  front  portion  of  the 
ring  projects  the  odontoid  process,  a  thick  bony  peg  arising 
from  the  axis  or  second  cervical  vertebra  (Fig.  32,  B^. 
Around  the  odontoid  process  the  atlas  rotates,  carrying 
the  head  with  it  from  side  to  side. 


Fig.  32. 

A  atlas.     B  atlas  and  axis,      a,  h  articulations  with  occipital  bone, 
c  transverse  ligament.      o  odontoid  process. 


43.  By  means  of  the  variations  in  the  form  of  the  ver- 
tebrae, and  by  the  four  curvatures  seen  in  the  spinal 
column,  a  considerable  range  of  movement  is  provided  for. 
The  vertebree  furnish  strong  support  for  the  great  mus- 
cles of  the  trunk  and  a  safe  channel  for  the  spinal  cord, 
while  a  firm  but  flexible  and  elastic  column  is  secured  for 
the  support  of  the  Avhole  frame. 

44.  The  Ribs. — Attached  by  their  heads  to  the  tho- 
racic vertebrae  are  the  twelve  pairs  of  slender  curved  bones 
called  ribs  (Fig.  33).  The  upper  seven  pairs  are  attached 
in  front  by  costal  cartilages  to  the  sternum^  or  breastbone. 
The  next  three  pairs  have  their  costal  cartilages  joined 
each  to  the  cartilage  of  the  preceding  rib  ;   A^•hile  the  last 


THE   FRAMEWORK   OF   THE   BODY  45 

two  pairs  have  their  front  cartilage  ends  unattached,  and 
are  therefore  called  floating  ribs.  All  the  ribs  have  a 
downward  slope,  their  front  ends  being  lower  than  the 
hinder  ones.  This  per- 
mits of  a  considerable 
enlargement  in  the  size 
of  the  cavity  of  the 
thorax^  or  chest,  when, 
by  the  contraction  of 
the  muscles  of  the 
chest,  the  front  ends 
of  the  ribs  are  raised. 
The  object  of  this  will 
be  shown  later. 

45.  The  Sternum,  or 
breastbone  (Figs.  27 
and  33),  supports  the 
forward  ends  of  the 
ribs  (with  the  excep- 
tion of  the  two  lowest, 
or    floating    ribs)  by 

means    of    the    costal  t.-„  oo      ei   i  4.       ,>  ^x.  ,      • 

Fig.  33.  — Skeleton  of  thorax,  showing  ribs, 

cartilages,  which  give      costal  cartilages,  sternum,  and  some  of  the 
more  freedom  of  move-     *^°^^^^°  vertebrae, 
ment  than  would  be  possible  were  the  bones  solid  to  the 
end.      The  sternum  is  composed,  in  the   adult,  of   three 
pieces,  the  lowest  being  of  cartilage. 

46.  The  Appendicular  Skeleton  is  composed  of  the  pectoral 
girdle^  the  pelvic  girdle^  and  the  bones  of  the  limbs. 

47.  The  Pectoral  Girdle  (Fig.  27)  consists  of  four  bones, 
two  on  each  side,  —  the  scapula  and  the  clavicle.  The 
scapula.,  or  shoulder  blade,  is  a  triangular,  nearly  flat 
bone  lying  at  the  back  of  the  shoulder  and  not  attached 


46  CONSCIOUS   NERVOUS   OPERATIONS 

directly  to  the  spinal  column.  It  has  a  shalloAv  pit  at  one 
of  the  uj)per  corners  for  the  end  of  the  humerus^  or  upper 
arm  bone,  and  a  projection  to  which  the  other  bone  of  the 
arch,  the  clavicle,  or  collar  bone,  is  secured.  The  clavicle 
is  a  round,  slender  bone,  attached  by  its  two  ends  to  the 
scapula  and  the  sternum. 

48.  The  Upper  Limbs  contain,  each,  thirty  bones.  They 
are  the  humerus^  or  upper  arm  bone  ;  the  radius  and  ulna^ 
side  by  side  in  the  lower  arm  ;  the  eight  small  bones  of 
the  carpus^  or  wrist  ;  the  five  cylindrical  bones  of  the 
metacarpus^  or  palm  of  the  hand ;  and  the  phalanges^  or 
finger  bones,  fourteen  in  number,  two  being  in  the  thumb 
and  three  in  each  other  finger. 

49.  The  Pelvic  Girdle  (Fig.  27)  is  formed  by  one  large 
spreading  bone  on  each  side,  called  the  os  innominatum^  or 
hip  bone.  On  the  outer  side  is  a  dee23  socket  for  the  head 
of  the  femur.  The  hip  bones  are  made  to  support  great 
weight  and  to  resist  severe  shocks.  They  sustain  the 
whole  pressure  of  the  trunk  and  of  burdens  carried,  and 
also  receive  the  force  of  the  various  movements  of  the 
lower  limbs,  as  in  running,  jumping,  cycling,  etc. 

50.  The  Lower  Limbs  are  similar  in  structure  to  the 
upper.  The  femur ^  or  thigh  bone,  the  largest  bone  in  the 
body,  corresponds  to  the  humerus  ;  the  tihia  and  fibula^ 
to  the  radius  and  ulna.  In  the  ankle  are  seven  tarsal 
bones^  and  in  the  arch  of  the  foot  five  metatarsals,  to  which 
are  added  the  fourteen  phalanges,  or  bones  of  the  toes. 
There  is,  besides,  a  bony  disk,  imbedded  in  the  great  liga- 
ment over  the  knee,  forming  a  protection  to  the  knee- 
joint,  and  called  the  patella,  or  kneepan. 

51.  Observe  the  provisions  in  the  human  skeleton  for 
securing  firmness  and  strength  to  the  upright  figure.  It 
has  been  found  that  the  arch   is   the  strongest  form  of 


THE   FRAMEWORK   OF   THE   BODY 


47 


structure  for  a  giveu  amount  of  material.  The  shoulder 
&rch  of  the  skeleton  furnishes  support  to  the  arms  so 
strong  that  those  limbs  may  be  used  to  lift  great  Aveights 
and  hurl  them  througli  the  air,  and  to  perform  a  great 
variety  of  labors.  The  pelvic  arch  and  the  arches  of  the 
foot  are  also  designed  to  support  securely  the  tall  human 
figure  and  to  carry  heavy  loads. 


52. 

Table  of  the  Bones. - 

- 

(.1)  Axial  Skeleton 

Frontal 
Parietal 

1 
2 

Cranium,  8 

Temporal 
Occipital 
Sphenoid 
Ethmoid 

Superior  Maxillary 
Inferior  Maxillary 

2 

1. 

Skull,  28 

Palate 
Xasal 

2 
2 

Face,  14 

Vomer 

Inferior  Turbinate 

Lachrymal 

Malar 

Malleus 
Incus 

1 
2 
2 
2 

2 

Bones  of  Ear,  6    . 

2 

Stapes 

2 

2. 

Hyoid,  1 

1 

'    Cer 

v'ical  Vertebrae 

7 

Doi 

sal  Vertebrae 

12 

3. 

Spinal  Column,  26           ^ 

Lun 

iibar  Vertebrae 

5 

Sac 

rum 

1 

,     Coc 

cyx 

1 

4. 

Thorax,  25 

j     Rib 

s 

24 

i     Stei 

rnum 

1 

48 


CONSCIOUS   NERVOUS   OPERATIONS 


(B)  Appendicular  Skeletox 


1.    Shoulder  Girdle,  4 

Clavicle 
Scapula 

Humerus 

2 

Ulna 

2 

2.    Upper  Extremities,  60 

Radius 
Carpals 

2 
16 

Metacarpals 

10 

Phalanges 

28 

3.    Pelvic  Girdle,  2 

Os  Innominatum 

2 

Femur 

2 

Fibula 

2 

. 

Tibia 

2 

4.   Lower  Extremities,  60 

Patella 

2 

Tarsals 

14 

Metatarsals 

10 

Phalanges 

28 

53.  Cartilage.  —  In  infancy  a  considerable  part  of  the 
skeleton  consists  of  cartilage,  or  gristle,  which  afterward 
becomes  ossified.  But  there  are  cartilages  —  such  as  the 
external  ear,  the  rings  around  the  windpipe,  and  the  ends 
of  various  bones  —  which  do  not  ossify,  and  are  known  as 
permanent  cartilages.  Cartilage  is  a  smooth  white  shining 
tissue  of  close  texture,  rarely  containing  blood  vessels. 
It  is  made  up,  like  the  bones,  of  cells  surrounded  by  the 
intercellular  substance  wliich  is  the  product  of  the  living 
cells.  A  thin  layer  of  cartilage  covers  the  surfaces  of 
the  bones  which  come  in  contact  with  other  bones.  Car- 
tilage also  serves  as  padding  in  various  parts  of  the  body. 

54.  Connective  Tissues  of  different  varieties  serve  to  com- 
plete the  skeleton.  They  form  the  strong  cords  and  bands 
and  sheets  called  ligaments,  for  binding  bones  together, 
and  the  tendons  whicli  fasten  the  muscles  to   the  bones. 


THE   FRAMEWORK   OF   THE   BODY 


49 


55.  Articulations. — All  unions  between  bones  are  called 
^articulations.  Some  of  these  allow  of  more  or  less  move- 
ment; others  permit  no  movemefit  at  all.  The  bones  of 
the  skull,  with  the  exception  of  the  lower  jaw  and  the 
minute  bones  belonging  to  the  inner  ear,  have  no  motion. 
In  most  cases  their  union  is  formed  by  means  of  toothed 
edges  which  fit  into  each  other,  forming  irregular  lines 
known  as  serrated  sutures.  They  lessen  jar  and  avert 
injury  to  the  brain.  The  different  vertebrae  of  the  spine 
have  a  very  slight  motion  upon  one  another,  due  to  the 
elasticity  of  the  cartilage  pads  or  cushions  which  sepa- 
rate them. 

56.  Joints.  —  Where  two  bones  are  articulated  in  such 
a  way  as   to  permit  one  bone  to   glide   freely  over  the 


Fig.  34.— Ball  and  socket  joint  at  hip. 

The  parts  are  separated  to  show  attachments  of  the  round  ligament. 

other,  the   union  is  called  a  joint.      Joints  are  of   vari- 
ous kinds  and  are  adapted  to  various  movements. 
macy's  phys.  — 4 


50 


CONSCIOUS   NERVOUS   OPERATIONS 


Fig.  35.  — Hinge  joint 
of  the  elliow. 

1  humerus.     2  ulua. 


The  hall  and  socket  joint  seen  in  the  shoulder  and  the 
hip  has  the  end  of  one  bone  fitted  into  the  hollow  of 
another,  and  provides  for  motion  in 
any  direction  (Figs.  34  and  86). 

The  2)ivot  joint  is  that  in  ^Yhich  one 
bone  rotates  round  another,  as  in  the 
atlas  and  axis  joint  (Fig.  32),  already 
described,  and  in  the  rotation  of  the 
ulna  on  the  radius  at  their  junction 
with  the  wrist. 

The  hinge  joint  permits  of  motion 
in  one  plane  only,  as  in  the  joints  of 
the  fingers.  Some  hinge  joints  have 
provision  for  additional  movements,  as 
in  the  elbow  (Fig.  35)  and  in  the 
articulation  between  the  lower  jaw 
and  the   skull. 

57.  Synovial  Membrane.  —  The  broad,  thin  ligament  sur- 
rounding a  joint  forms  a  closed  sac.  This  sac  is  lined 
with  the  synovial  membrane^  which  secretes  a  fluid  whose 
purpose  is  to  lubricate  the  joint,  as  oil  lubricates  the  parts 
of  a  machine  which  move  upon  one  another  (Fig.  36). 

58.  Structure  of  Bone.  —  A  living  bone  is  tough,  strong, 
and  slightly  elastic.  Bnrned  in  a  fire  it  retains  its  size 
and  shape,  but  becomes  brittle  and  easily  crumbles  to  pow- 
der. Soaked  for  a  few  days  in  dilute  muriatic  acid,  it  also 
retains  its  shape,  but  becomes  so  flexible  that,  if  one  of  the 
long  bones,  it  may  be  tied  in  a  knot.  The  fire  destroys 
the  33  per  cent  of  animal  matter  in  the  bone,  leaving  the 
calcium  phosphate,  calcium  carbonate,  and  the  small  quan- 
tities of  other  salts  which  constitute  the  earthy  or  mineral 
portion  of  bone.  The  acid  dissolves  out  the  earthy  salts 
and  leaves  the  animal  tissues. 


THE   FRAMEWORK   OF   THE    BODY 


51 


On  examination,  one  of  the  long  bones  in  a  fresh  condi- 
tion is  seen  to  be  covered  at  the  two  ends  with  smooth 
white  articular  cartilage^  while  the  shaft  is  inclosed  in  a 
sheath  of  dense  wliite  fibrons  membrane,  called  the  peri- 
osteum^ closely  adhering  to  it.  It  is  on  the  inner  side  of 
this  membrane  that  the  bone  grows,  and  by  it  the  nutri- 


Pelvic  Bone 
Synovial  Membi^ane 


Head  of  Femur 
Round  Ligament 


Capsular  Ligament 


Fig.  36.  —  Section  of  hip  joint. 

tion  of  the  bone  throughont  life  is  assisted.  If  the  peri- 
osteum is  torn  away,  the  bone  dies.  It  covers  every  part 
of  the  snrface  of  a  bone  not  covered  by  the  articnlar  car- 
tilage, and  into  it  the  fibers  of  the  ligaments  extend,  being 
so  interwoven  as  to  make  an  indistinguishable  and  insep- 
arable junction. 

59.  Inner  Composition  of  Bone. : —  If  the  bone  is  sawn 
through  from  end  to  end,  the  shaft  is  found  to  be  hollow, 
with  the  medullary  cavity^  as  it  is  called,  in  the  center, 
filled  with  yelloiv  marrow.  The  walls  of  the  shaft  are 
of  a  dense,  solid  structure,  except  for  a  thin  stratum  of 


52 


CONSCIOUS   NEKVOUS   OPERATIONS 


spongy  bone  around  the  cavity  which  contains  the  mar- 
rov/  (lower  end  of  Fig.  37). 

In  the  enlarged  articular  extremities  of  the  bone,  how- 
ever,  the   reverse   is  the   case.     The   firm,  compact  part 

forms  only  a  thin 
layer  on  the  sur- 
face, the  rest  being 
a  loose,  spongy  net- 
work of  bony  mat- 
ter, with  the  spaces 
filled  with  a  soft, 
red  substance  called 
red  marrow. 

Interlacing  chan- 
nels, called  the  Ha- 
versian canals,  run 
through  the  whole 
substance  of  ^  bone, 
in  the  densest  as 
in  the  more  porous 
parts.  The  perios- 
teum is  richly  sup- 
plied with  blood  ves- 
sels, and  from  them 
minute  branches  en- 
ter the  bone  itself 
and  run  along  the 
Haversian  canals. 
Other  V)lood  vessels  reach  the  solid  portion  of  the  bone 
from  within,  through  the  medullary  canal  of  the  center  of 
the  bone,  and  thus  nutriment  is  conveyed  to  every  part. 

Each  Haversian  canal  is  surrounded  by  a  set  of  hard 
bony  plates,  and  between  the  plates,  or  lamelhe,  are  little 


Fig    37. 


Longitudinal  section  of  the  upper 
end  of  the  tibia. 


THE   FRAMEWORK   OF   THE    BODY  53 

cavities  called  Jaeunce,  connected  by  minute  canals  with 
owe  another  (^Fig.  16,  p.  25).  Within  the  lacuna3  and 
their  canals  are  found  little  masses  of  protoplasm  called 
hone  cells,  or  hone  corpuscles.  These  branching  bone  cells 
communicate  with  one  another  and  with  the  blood  vessels 
of  the  Haversian  canals.  They  are  the  architects  for 
building  up  the  bony  fabric.  Each  cell  constructs  walls 
Avhich  unite  with  those  about  them  to  form  the  solid  mass. 
Along  with  the  arteries  of  the  interior  bony  structure 
very  line  nerve  fibers  have  been  traced,  and  lymph  vessels 
are  found  in  connection  with  the  blood  capillaries  within 
the  substance  of  all  bones. 

60.  Hygiene  of  Bones  and  Joints.  —  The  science  of  hygiene 
has  to  do  Avith  all  that  promotes  normal  action  of  the 
various  parts  of  the  body  and  of  the  whole  mechanism. 
In  respect  to  the  bones  we  need  to  consider  first  the  con- 
ditions most  favorable  to  their  growth. 

61.  Bones  of  the  Young. — As  the  skeleton  grows  it  not 
onlv  becomes  laro-er,  but  also  becomes  chano'ed  in  the  struc- 
tore  of  its  parts.  The  bones  of  an  infant  are  almost  wholly 
composed  of  cartilage,  having  the  form  of  the  completed 
bone,  but  the  flexibility  and  elasticity  of  the  cartilaginous 
tissue.  They  become  slowly  more  firm  and  liard  by  a 
deposit  of  solid  material  furnished  by  the  food,  selected 
from  the  blood  and  lymph  by  the  living  cells  in  the  carti- 
lage and  the  periosteum.  As  the  bone  is  built  up  by  the 
deposit  of  the  salts  of  lime  (chiefly  calcium  phosphate), 
which  furnish  nearly  all  the  earthy  part  of  bone,  the  carti- 
lage cells  waste  awa}',  and  their  dead  matter  is  carried  ofl: 
by  the  blood. 

62.  Importance  of  Proper  Food.  —  It  is  evident  that  the 
food  suitable  for  young  children  must  contain  lime  and 
phosphorus  in  proper  proportions  for  making  bone.    Milk 


54  CONSCIOUS   NERVOUS   OPERATIONS 

has  been  found  to  furnish,  in  most  digestible  form,  those 
substances  and  others  needed  by  the  human  infant,  and 
is  for  early  childhood  the  complete  and  perfect  food.  If 
there  is  not  a  sufficient  supply  of  earthy  matter  in  the  food, 
the  bones  of  a  child  remain  soft  and  weak,  and  are  easily 
bent  or  deformed,  as  in  the  disease  cslled  rickets.  For  such 
conditions  an  abundance  of  suitable  food,  with  plenty  of 
fresh  air  and  sunshine,  supplies  the  cure. 

Alcohol  and  tobacco  are  particularly  to  be  avoided  dur- 
ing the  time  of  growth,  as  they  retard  or  prevent  the  full 
development  of  the  bone  cells,  making  the  figure  stunted 
and  enfeebled.     Cigarettes  are  especially  harmful. 

63.  Deformity  to  be  Guarded  Against.  —  Children  permitted 
to  walk  too  early,  before  the  bones  are  sufficiently  hardened, 
may  be  made  permanently  bow-legged.  They  should  be 
allowed  freedom  of  movement  and  plenty  of  exercise,  but 
should  not  be  urged  to  walk  too  soon. 

Long-continued  pressure  upon  the  bones  of  cMldren 
may  result  in  deformity.  Some  tribes  of  Indians  flatten 
the  heads  of  their  children  by  fastening  boards  upon  them. 
Clothing  should  always  be  loose ;  shoes  especially  should 
allow  room  for  movement  and  growth. 

Care  should  be  taken  that  a  child  should  habitually 
assume  correct  positions  in  sitting  and  standing,  and  fre- 
quent changes  of  position  are  needful.  The  seat  should 
not  be  too  high  to  permit  the  feet  to  rest  easily  and 
squarely  upon  the  floor,  otherwise  the  bones  of  the  thigh 
may  be  bent  by  the  weight  of  the  legs.  School  children 
should  be  tauglit  to  sit  upright  while  writing  or  studying, 
lest  the  spine  become  curved  and  diseased.  Seats  and 
desks  should  be  carefully  adapted  to  the  child's  stature, 
and  round  shoulders  —  the  most  common  deformity  — 
should  Ije  especially  guarded  against. 


THE   FKAMEWORK   OF   THE    BODY  36 

In  standing,  the  weight  should  be  supported  evenly  by 
the  two  feet.  One  hip  or  one  shoulder  often  becomes 
higher  than  the  other,  upsetting  the  firm  poise  of  the 
figure  by  neglect  of  this  precaution.  A  teacher  should 
see  that  a  child  is  not  kept  standing  till  wearied. 

64.  Bones  of  the  Aged.  —  As  the  bones  of  the  young  con- 
tain an  excess  of  animal  matter,  so  those  of  the  old  have 
an  excess  of  mineral  substances  and  are  consequently 
more  brittle.  The  aged,  therefore,  need  to  guard  espe- 
cially against  fractures  of  the  bones.  Not  only  are 
their  bones  more  easily  broken,  they  are  also  healed  with 
greater  difficulty.  In  the  young  and  healthy  the  vital 
processes  are  more  actively  carried  on,  and  the  busy  bone 
cells  go  swiftly  to  work  to  repair  a  breakage,  throwing 
out  iirst  around  the  injured  parts  a  soft  repairing  material 
in  which  bony  matter  is  afterward  deposited ;  but  in  the 
aged  the  bone  cells  work  slowly,  and  a  broken  bone  is 
sometimes  never  fully  restored. 

65.  Broken  Bones.  —  The  two  ends  of  a  broken  bone 
should  be  brought  together  into  their  correct  position  as 
soon  as  possible,  before  inflammation  and  swelling  render 
this  difficult.  Of  course  a  skillful  surgeon  should  be 
called  to  "  set "  a  broken  bone  ;  but  there  may  be  delay, 
—  the  patient  may  have  to  be  carried  some  distance.  In 
such  cases  care  should  be  taken  to  prevent  injury  to  the 
surrounding  parts  from  the  fractured  ends  of  the  bone. 
A  limb  should  be  bound  to  a  strip  of  board  or  even  an 
umbrelhi  as  a  temporary  splint. 

66.  Injuries  to  Joints.  —  Dislocation  of  a  joint  stretches 
or  breaks  the  ligaments  and  other  membranes  around 
it,  producing  inflammation.  This  renders  examination 
and  putting  in  place  difficult,  and  a  dislocated  joint 
should  therefore  be  restored  to  place  as  soon  as  the  need- 


56  CONSCIOUS   NERVOUS   OPERATIONS 

ful  skill  can  be  procured.  A  sprain,  which  is  a  sudden 
wrenching  or  straining  of  the  ligaments  not  sufficient  to 
dislocate  the  joint,  is  often  as  serious  as  a  dislocation. 
Neither  should  be  neglected  or  treated  lightly.  Inflamma- 
tion, if  not  checked,  sometimes  results  in  the  destruction 
of  the  synovial  fluid  and  the  coverings  of  the  ends  of  the 
bones  in  the  joints,  and  consequently  in  permanent  stiff- 
ness of  the  joint.  Immediate  and  long-continued  rest  is 
imperative,  and  competent  surgical  advice  should  usually 
be  secured. 

Demonstrations  and  Experiments 

10.  The  Skeleton.  —  For  the  study  of  the  osseous  system  there  should 
be  accessible  to  the  student  a  mounted  human  skeleton.  In  absence 
of  this,  a  mounted  skeleton  of  a  cat  or  dog  may  be  used.  Whefi^e  the 
school  property  does  not  include  a  skeleton  of  any  kind,  the  enthusi- 
astic teacher  will  provide  one.  This  can  be  very  quickly  done  as  fol- 
lows. Clean  most  of  the  flesh  from  the  skeletal  of  a  cat,  ^og,  or 
rabbit ;  boil  the  partly  cleaned  skeleton  in  "  liquid  soap,"  one  part, 
and  water,  four  parts,  for  forty  minutes,  then  for  thirty  minutes  in 
liquid  soap  and  water,  equal  parts ;  cool  the  skeleton  in  cold  water ; 
clean  with  a  brush  and  allow  to  dry.  The  liquid  soap  is  made  by 
dissolving  12  grams  of  saltpeter  and  75  grams  of  white  soap  in  a  mix- 
ture of  2000  cubic  centimeters  of  water  and  150  cubic  centimeters  of 
strong  ammonia. 

The  skeleton  may  be  studied  without  any  attempt  at  mounting  it. 
The  student  should  follow  the  text  of  this  chapter,  identifying  each 
bone  as  it  is  described.  The  teacher  will  find  it  profitable  to  have  each 
student  "  demonstrate  "  the  whole  or  a  certain  part  of  the  skeleton, 
i,e.  point  out  and  name  the  various  parts  without  any  reference  to  the 
text  and  without  leading  questions  from  the  teacher. 

11.  Cartilage.  —  At  a  meat  market,  bones  can  be  procured  which 
will  show  hyaline  cartilage  on  their  articular  surfaces.  At  a  slaughter- 
house can  be  obtained  the  windpipe,  ears,  costal  cartilages,  etc.,  of 
various  animals,  and  the  general  appearance  and  purposes  of  the  dif- 
ferent varieties  of  cartilaue  can  be  shown  from  them.     To  show  the 


THE   FRAMEWORK   OF   THE   BODY  57 

minute  structure  of  cartilage,  cut  very  thiu  sections  with  a  razor  from 
the  articular  surface  of  a  fresh  bone  of  a  young  animal,  mount  in 
normal  salt  so-lution,  and  examine  with  the  compound  microscope. 

12.  Structure  of  Bone.  —  Procure,  at  a  meat  market,  a  leg  bone  of 
some  animal  and  compare  it  in  appearance  with  a  similar  bone  that 
has  been  exposed  to  the  weather  for  months.  Observe  the  pink  color 
of  the  fresh  bone,  and  the  fibrous  periosteum  that  covers  it.  Saw 
the  two  bones  open  lengthwise  and  observe  the  marrow  cavity  in  each. 
Notice  the  compact  shaft  of  each,  and  the  cartilage  on  the  articular 
surface  of  the  fresh  bone. 

13.  Minute  Structure  of  Bone.  —  Mounted  sections  of  bone  may  be 
procured  of  dealers  in  microscopical  supplies,  or  the  teacher  may  pre- 
pare them  by  sawing  thin  pieces  from  the  shaft  of  a  dry  weathered 
bone  and  then  filing  them  down  till  they  are  extremely  thin.  They 
may  be  mounted  in  water  on  a  slide  and  examined  wdth  the  micro- 
scope. But  a  better  way  is  to  dry  the  sections  thoroughly,  after  care- 
fully washing  them  in  alcohol,  and  then  to  mount  them  in  Canada 
balsam  that  has  been  evaporated  until  it  solidifies  on  cooling.  The 
sections  should  be  quickly  placed  in  the  hot  balsam  upon  a  clean  slide, 
covered  wdth  a  cover  glass,  and  cooled  to  harden  the  balsam. 

14.  Composition  of  Bone.  — Two  pieces  of  the  same  fresh  bone  or  two 
similar  fresh  bones  should  be  obtained.  Burn  one  piece  in  a  fire  for 
several  hours  till  it  turns  completely  white.  All  the  animal  matter 
has  been  removed.  Place  the  other  piece  of  bone  in  w^eak  muriatic 
acid  (10-15*per  cent  strength)  for  several  days  to  decalcify.  It  becomes 
soft,  owing  to  the  removal  of  the  mineral  matter.  Observe  the  brittle- 
ness  of  the  burned  bone,  and  the  toughness  and  flexibility  of  the  other 
piece.  Place  the  burned  bone  in  the  muriatic  acid,  and  burn  the  piece 
of  decalcified  bone.     What  is  left? 

15.  .Joints.  —  The  various  kinds  of  joints  can  be  demonstrated  on  a 
skeleton.  The  actual  movements  that  occur  at  those  joints  should  be 
performed  by  the  student  in  corresponding  joints  of  his  owai  body. 

16.  Dissection  of  a  Joint.  — ^  Procure  a  leg  joint  of  a  sheep  and  show^ 
the  possible  movements  of  the  bones  that  form  the  joints.  Observe  the 
tendinous  attachments  of  muscles,  also  the  ligaments  that  hold  the 
bones  together.  Cut  through  the  ligaments  and  open  the  joint  cavity. 
Notice  the  synovial  fluid,  and  the  cartilage  on  the  articular  surfaces 
of  the  bones. 


Fig.  38.— The  muscular  system, 

58 


CHAPTER  V 


THE  MUSCULAR  SYSTEM 


67.  Though  the  skeleton  preserves  the  shape  of  the 
body,  the  muscles  with  the  surrounding  fat  fill  out  the 
figure,  giving  roundness  and  grace  of  outline.  Muscles 
and  bones,  with  the  tendons  and  ligaments  connecting 
them,  constitute  the  organs  of  motion  and  locomotion: 
they  are  the  apparatus  by  means  of  wdiich  the  nervous 
system  acts  when  the  object  sought  is  movement ;  as  the 
stomach,  liver,  blood  vessels,  kidneys,  and  other  parts 
of  the  digestive  system  are  the  apparatus  w^hich  the  nerv- 
ous system  uses  for  the 
purpose  of  nutrition. 

68.  The  Muscles  are  the 
lean  part  of  meat.  They 
make  up  that  part  of  the 
body  which  w^e  call  flesh. 
When  a  muscle  is  exam- 
ined, it  is  found  to  consist 
of  small  fibers  bound  to- 
gether in  bundles  (Fig. 
39),  each  bundle  being 
wrapped  in  a  thin  sheath 
of  areolar  tissue,  called  i^erimysiumy  wliile  eacli  minute 
fiber  of  which  a  bundle  is  composed  lias  also  its  mem- 
branous   sheath,  called  the  sareolemma. 

50 


Fig.  39— Bundles  cf  striatea 

muscle  cut  across. 

ff  several  bundles  bound  together  into 

larger  bundles  to  make  up  the  nuiscle. 


60 


CONSCIOUS   NERVOUS   OPERATIONS 


Fig.  40.  — Pieces  of 
striated  muscle 
fibers. 

Showing  the  spin- 
dle -  shaped  nuclei 
and  cross-striations. 
At  the  left  above  is 
the  rounded  end  of  a 
liber. 


69.  Classification. — The  muscles  are  divided  into  two 
classes,   usually  called  the  voluntary  and  the  involuntary 

muscles,  the  first  being  under  the  con- 
trol of  the  will,  while  the  second  are  not. 
There  is  also  a  difference  under  the 
microscope  between  the  two  classes  of 
muscles.  Voluntary  muscular  tissue  is 
composed  of  fibers  which  are  marked  by 
alternate  dark  and  light  stripes.  They 
are  called  striated  or  striped  muscular 
fibers  (Fig.  40).  The  fibers  which  com- 
pose the  involuntary  muscles  are,  as  a 
rule,  destitute  of  these  markings  and 
are    called  plain   muscular    fibers  (Fig. 

41). 

Certain  exceptions  to  the  above  rule 
should  be  noted.  The  muscles  of  the  heart,  though  not 
under  the  control  of  the  will,  are  made  up  of  Griped 
muscular  fibers  ;  and  also  the  muscular  fibers  found  in 
the  pharynx,  part  of  the  esophagus,  and  in  the  internal 
ear,  though  involuntary,  have  the  structure  of  voluntary 
muscle   fiber.      On   the   other  hand,   the    ciliary  muscles, 

by  which  the  eye  is  accom-  

modated  for  seeing  objects        ^         ^"^ 
at  different  distances,   are  Fig.  41 .  — Plain  muscle  fiber, 

under    the    control  of  the  iVMmcieus. 

will,    though    composed    wholly    of    j^lain    or    unstriped 
muscle  fibers. 

Some  striped  muscles,  like  those  of  respiration  and  of 
the  eyelids,  are  partly  voluntary  and  partly  involuntary. 

70.  Voluntary  Muscles. — These  are  also  called  skeletal 
muscles,  because  they  constitute  the  muscular  apparatus 
attached  to  the  bones.     Each  muscle  is  usually  larger  in 


THE   MUSCULAR    SYSTEM 


61 


the  middle  than  at  the  ends,  and  the  swollen  middle 
'  portion  is  called  the  helly.  The  belly  is  usually  unat- 
tached, but  the  two  ends  are  secured  to  the 
bones  by  tendons  which  are  continuous 
with  the  connective  tissue  of  the  muscle 
(Fig.  42). 

Between  the  small  fibers  of  the  bundles 
which  make  up  a  muscle  is  a  little  loose 
areolar  tissue  in  which  are  distributed  the 
blood  A^essels  and  nerves  for  the  muscle. 

71.  Muscle  Cells  or  Muscle  Fibers.  — It  is  in 
the  microscopic  threads  of  the  muscle  that 
the  peculiar  power  of  contraction  lies. 
These  are  variable  in  length  and  thick- 
ness, but  are  said  to  average,  in  voluiitary 
muscles,  -^^-^  of  an  inch  in  diameter  and 
about  one  inch  in  length.  They  are  cylin- 
drical in  shape,  with  rounded  ends  (Fig. 
40),  and  as  a  rule  do  not  branch.  In 
the  muscles  of  the  face  and  tongue,  how- 
ever, the  muscle  fibers  divide  into  many 
branches. 

Each  muscle  fiber^  or  cell^  consists  of  the   i  tendinous  ends. 
sarcolemma  and  a  soft,  semifluid  material  of  *"    ^  ^' 
alternate  light  and  dark  disks,  called  the  contractile  sub- 
stance.      Just  beneath  the  sarcolemma    are   several  long 
oval  nuclei. 

72.  Nerve  Endings  in  Muscle  Fiber. —  It  is  impossible  to 
treat  of  muscles  and  their  action  without  including  some 
study  of  the  other  sort  of  irritable  tissue,  ney^vous  tissue^ 
upon  which  muscular  action  depends. 

The  sarcolemma  of  each  muscle  fiber  is  pierced  by  a 
branch  of  a  nerve  fiber.     The  primitive  sheath  or  neuri- 


Fig.  42.  — Biceps 
muscle. 


62 


CONSCIOUS   NERVOUS   OPERATIONS 


Fig.  43.  —Nerve  endings  in  stri 
ated  muscle  fibers. 


lemma  (the  inclosing  membrane  of  the  nerve  fiber)  becomes 
continuous  with  the  sarcolemma,  and  the  axis  cylinder  of 

the  nerve  fiber  branches  many 
times,  the  ramifications  end- 
ing in  a  flat  or  branched  layer 
of  protoplasm  containing  nu- 
clei. These  terminal  nerve 
organs  are  called  end  plates 
(Figs.   43  and  44). 

73.  How  a  Muscle  Contracts. 
—  A  muscle  contracts  or  be- 
comes shorter  in  proportion  to 
its  length,  without  change  in 
bulk,  under  the  influence  of  stimulus.  It  is  the  office  of 
the  nerves  of  the  muscles  to  carry  to  them  their  natural 
stimulus,  but  muscles  also 
contract  under  the  action 
of  other  stimuli;  for  in- 
stance, in  consequence  of 
a  sudden  blow  or  pinch, 
when  heat  is  applied  sud- 
denly, when  certain  chemi- 
cal substances  are  dropped 
upon  them,  or  when  an 
der  trie  shock  is  conducted 
to  them. 

In  living  animals  the 
muscles  are  always  more 
or  less  contracted.  This 
is  due  to  the  nervous  influence  which  they  constantly 
receive.  If  their  nerves  are  cut  or  destroyed,  the  mus- 
cles lengthen.  This  tension  of  the  muscles  keeps  them 
ready  for  immediate  action.     When   a   nervous  impulse 


Fig.  44— Motor  nerve  endings  in 
striated  muscle  fibers. 


THE    MUSCULAR    SYSTEM  68 

reaches  a  muscle,  the  nuinerous  branches  of  the  nerve 
—  one  for  each  individual  muscle  cell  —  distribute  the 
stimulus  to  all  parts  at  practically  the  same  instant. 
The  end  plates  are  situated  in  each  muscle  fiber  near 
the  middle  between  the  two  ends,  and  the  fiber  begins 
there  to  contract.  The  two  ends  draw  toward  each 
other ;  the  liber  becomes  swollen  and  shorter.  In  the 
muscle  as  a  whole  contraction  is  simply  the  sum  of  the  con- 
tractions of  all  the  minute  fibers  which  compose  it.  In 
the  muscle  liber  contraction  appears  to  be  some  compli- 
cated movement  of  the  molecules  which  produces  a  change 
in  the  appearance  of  the  stripes.  It  is  found  that  in 
those  places  where  swift  and  rapid  contraction  is  called 
for,  the  muscular  tissue  has  almost  invariably  the  striped 
fibers. 

74.  When  a  muscle  is  made  to  contract  by  a  single 
electric  shock,  or  by  other  artificial  means,  the  movement 
is  sudden  and  brief.  Voluntary  muscle,  however,  under 
its  natural  nervous  stimulus,  never  contracts  with  a 
twitch.  Its  action  is  rather  that  of  continued  gentle 
vibration,  called  tetanus,  such  as  follows  a  rapid  series 
of  electric  shocks  which  leave  no  time  for  relaxation. 
The  nervous  stimulus  comes  to  the  muscle  in  a  quick 
succession  of  impulses,  —  about  twenty  in  a  second,  — so 
that  one  vibration  is  succeeded  by  a  second  before  the 
first  has  ceased  to  agitate  the  muscle  cell. 

75.  Internal  Changes  in  Muscle  under  Stimulus.  —  Some  of 
the  energy  set  free  by  a  contracting  muscle  appears  as  work 
done,  weight  lifted,  etc.,  while  a  considerable  amount 
becomes  heat,  for  the  temperature  of  muscle  always  rises 
under  contraction.  Certain  chemical  changes  also  ap- 
pear. Variable  amounts  of  carbonic  acid  and  lactic  acid 
are  set  free,  and  oxygen   is  used   up.      Electric  changes 


64  CONSCIOUS   NERVOUS   OPERATIONS 

lasting  for  some  time  are  also  produced  in  the  muscle 
by  its  contraction.  These  are  shown  by  the  use  of  a 
delicate  galvanometer. 

76.  Another  imj^ortant  effect  upon  itself  of  a  muscle's 
contraction  is  what  we  call  fatigue  of  the  77iuscles,  that  is, 
a  lack  of  readiness  to  respond  to  stimulus.  This  is  due 
to  the  using  up  of  the  material  in  the  muscles  which  was 
available  for  the  production  of  energy,  and  still  more  to 
the  accumulation  of  waste  matter  —  the  product  of  the 
activity  of  the  muscles.  Experiments  have  shown  that  it 
is  not  the  muscle  itself  which  first  becomes  too  much 
fatigued  for  contraction.  Nor  is  the  seat  of  fatigue  in 
the  nerve,  but  m  the  end  plate  within  the  muscle  cell.  The 
fatigue  is  relieved  by  even  a  brief  rest,  and  such  relief  is 
absolutely  necessary  to  the  health  of  the  muscles.  Even 
the  muscles  of  the  heart,  that  organ  which  works  cease- 
lessly from  the  beginning  of  life  to  death,  have  a  period 
of  rest  after  each  beat.         .  * 

77.  External  Effects  of  Muscular  Contraction  and  Relaxation. 
—  The  purpose  of  muscular  contraction  is  the  production 
of  motion.  The  contraction  and  relaxation  of  the  muscular 
walls  of  the  heart  keep  the  blood  in  constant  movement  ; 
the  various  other  vital  processes  are  also  dependent  upon 
more  or  less  constant  motion  in  the  tissues  and  organs  of 
the  body,  and  all  our  outward  activities  are  likewise  the 
results  of  the  shortening  and  lengthening  of  the  innumer- 
able strands  of  muscular  tissue. 

Muscular  power,  or  the  amount  of  force  which  a  mus- 
cle can  supply,  varies  with  its  health  and  vigor,  and  with 
its  form.  The  thickest  muscles  can  lift  the  heaviest 
load.  Those  having  the  longest  strands  can  move  a 
weight  the  greatest  distance.  Hence  the  human  body 
possesses  both  long,  slender  muscles,  and  short,  stout  ones, 


THE    MUSCULAR    SYSTEM  65 

as  well  as  those  of  all  sizes  and  lengths  between.  Many 
muscles  which  we  might  at  first  think  to  be  long  are 
really  short,  but  appear  long  because  of  the  long  tendons 
by  which  they  are  attached  to  the  bones.  Many  of  the 
muscles  which  move  the  fingers,  for  example,  have  their 
bellies  in  the  forearm,  and  are  attached  to  the  small  bones 
of  the  fingers  by  long,  slender  tendons.  The  force  with 
which  muscles  contract  is  sometimes  very  great.  A  human 
muscle  one  square  centimeter  (.15  square  inch)  in  section 
can  raise  a  weight  of  5(370  grams  or  200  ounces. 

When  a  muscle  contracts,  its  two  ends  are  drawn  nearer 
together,  and  hence  draw  toward  each  other  the  parts  to 
which  the  ends  of  the  muscle  or  its  tendons  are  attached  ; 
the  belly  of  the  muscle  becomes  swollen,  and  in  strong 
contraction  the  Avliole  muscle  becomes  tense  and  hard. 

78.  Contraction  is  speedily  follow^ed  by  relaxation.  The 
stimulating  force  ceases  to  be  supplied,  and  the  muscle 
returns  to  a  state  of  rest.  If  the  hand  has  been  raised  by 
the  contraction  of  the  hiceps  muscle  on  the  inner  side  of 
the  humerus,  it  will  fall  under  the  action  of  gravitation 
when  that  contraction  ceases  and  the  muscle  becomes 
passive.  In  order  that  the  hand  may  be  drawn  down 
with  force  the  action  of  the  triceps  muscle  at  the  back  of 
the  humerus  is  needed.  Muscles  can  give  a  powerful  pull^ 
but  they  cannot  push.  Very  generally,  therefore,  they 
are  arranged  so  that  muscles  which  cause  movement  in 
one  direction  are  opposed  by  those  which  cause  movement 
in  the  opposite  direction. 

79.  Dead  Muscle.  —  The  muscles  of  a  dead  body,  or 
muscles  which  have  been  removed  from  a  living  body, 
gradually  undergo  a  marked  change,  which  results  in 
the  stiffening  known  as  rigor  mortis.  That  which  was 
translucent  becomes   more    opaque,   most  of  the   natural 

MACV'S    PHYS. 5 


66  CONSCIOUS  NERVOUS   OPERATIONS 

elasticity  disappears,  and  a  hard,  rigid  condition  sets  in, 
accompanied  by  more  or  less  contraction.  This  is  due  to 
a  coagulation  of  the  protoplasm  of  the  muscle  cells,  simi- 
lar to  the  clotting  of  blood.  Rigor  mortis  passes  away 
after  a  time,  and  the  dead  body  becomes  soft  and  flabby 
—  a  sign  of  approaching  decay. 

80.  Plain  or  Involuntary  Muscles.  — Though  the  plain 
muscles  are  not  under  the  control  of  the  will,  they  still 
have  nervous  connection  with  the  central  nervous  system. 
Most  of  the  nerves  supplying  the  organs  having  plain  or 
unstriped  muscular  tissue  come  from  the  sympathetic  nerv- 
ous system;  but  from  every  ganglion  of  the  sympathetic 
chain  nerve  fibers  communicate  with  the  brain  and  spinal 
cord.  The  muscles  of  the  blood  vessels,  lymphatics, 
glands,  and  other  internal  organs,  are  of  unstriped  struc- 
ture, and  carry  on  their  work  without  affecting  conscious- 
ness. Their  action  under  stimulus  is  similar  to  that  of 
the  skeletal  muscles,  but  takes  place  much  more  slowly. 

81.  Plain  Muscle  Fibers.  —  Plain  muscles  are  made  up, 
like  skeletal  muscles,  of  bundles  of  fibers,  and  these  of 
muscle  cells.  The  cells,  however,  differ  from  those  of  the 
voluntary  muscles.  They  are  long,  spindle-shaped  fibers, 
having  a  rod-shaped  nucleus  in  the  center  (Fig.  41).  The 
nerves  of  plain  muscle  fibers  do  not  end  in  end  plates,  but 
form  plexuses^  or  networks,  which  ramify  between  and 
around  the  muscle  fibers.  The  nerves  of  the  heart  mus- 
cles end  as  do  those  of  the  unstriped  muscles. 

82.  Rhythmic  and  Peristaltic  Movements  of  Involuntary  Mus- 
cle. —  One  of  the  characteristics  of  involuntary  muscles  is 
a  tendency  to  alternate  regular  periods  of  activity  and 
rest.  The  heart  is  the  most  familiar  illustration  of  this 
rhythmical  tendency,  but  it  is  seen  in  some  other  organs, 
and  especially  in  some  of  the  lower  animals. 


THE   MUSCULAR   SYSTEM  67 

The  peristaltic  action  of  plain  muscle  is  seen  in  the 
small  intestine  and  in  other  parts  of  the  alimentary  canal. 
When  any  part  of  the  tube  is  stimulated,  a  circular  con- 
traction results,  which  slowly  passes  along  in  a  wavelike 
manner  through  the  length  of  the  tube.  In  the  diges- 
tive tract  this  movement  serves  to  drive  the  food  onward. 

83.  Involuntary  muscle,  as  a  rule,  contracts  more  slowly 
than  voluntary  muscle.  It  contracts,  not  with  a  tetanus 
like  that  of  voluntary  muscle,  but  with  a  single,  much 
prolonged  contraction. 

84.  Mechanism  of  Movement.  —  The  power  of  the  muscles 
to  change  their  form  carries  with  it  the  power  to  change 
the  positions  of  the  bones  and  other  parts  of  the  body  to 
which  they  are  attached,  and  hence  to  change  the  positions 
of  the  different  parts  in  respect  to  one  another  and  to  move 
the  whole  frame  from  place  to  place. 

When  a  part  of  the  body  is  moved  at  a  joint,  the  bone 
which  is  moved  acts  as  a  lever.  A  lever  is  a  stiff  bar 
which  can  be  moved  round  a  fixed  point,  or  fulcrum. 
Three  classes  of  levers  are  known  to  the  science  of 
mechanics,  depending  upon  the  position  of  the  fulcrum 
with  reference  to  the  weight  to  be  moved  and  the  power 
which  produces  the  motion.  In  the  first  class  the  fulcrum 
is  between  the  weight  and  the  power,  as  in  using  a  crowbar 
to  lift  the  edge  of  a  stone.  In  the  second  class  the  ful- 
crum is  at  one  end,  the  power  at  the  other,  and  the  weight 
between  them.  In  the  third  class  the  fulcrum  is  at  one 
end,  the  weight  at  the  other,  and  the  power  is  applied 
between  the  two.  All  three  forms  of  levers  are  found  in 
the  human  body,  though  the  levers  of  the  third  class  are 
the  most  numerous  (Fig.  45). 

85.  Lever  of  the  First  Class.  —  The  action  of  a  lever  of 
the  first  class  is  seen  in  the  straightening  of  the  bent  arm. 


68 


CONSCIOUS   NERVOUS   OPERATIONS 


The  muscle  at  the  back  of  the  humerus  applies  the  power. 
It  is  attached  by  tendons  to  the  scapula  and  to  the  hinder 
side  of  the  humerus,  while  the  tendon  into  which  the  lower 
end  of  the  muscle  narrows  is  inserted  into  the  end  of  the 
ulna  at  the  elbow,  which  is  more  than  an  inch  above  the 
articulation  of  the  ulna  with  the  humerus.  By  its  contrac- 
tion the  muscle  pulls  the  upper  end  of  the  ulna  upward,  draw- 
ing down  the  hand,  which  is  the  weight  at  the  lower  end  of 
the  ulna,  and  straightening  the  joint.  The  fulcrum  is  at 
the  elbow  joint,  between  the  hand  and  the  power  at  the 
upper  end  of  the  ulna. 


I  II  III 

Tig.  45.  —  Diagram  of  the  foot,  illustrating  levers  of  the  three  classes. 

I  tapping  the  toe  on  the  floor.        II  rising  on  the  toes. 
Ill  lifting  a  weight  with  the  toes. 


86.  Lever  of  the  Second  Class.  —  When  the  body  is  raised 
on  the  toes  (Fig.  45,  I  J)  the  action  of  a  lever  of  the  second 
class  is  seen.  The  weight  is  that  of  the  whole  body  sup- 
ported by  the  foot  at  the  ankle,  while  the  power  operates 
through  the  muscles  of  the  calf  of  the  leg  at  the  heel,  the 
toes  acting  as  the  fulcrum. 

87.  Lever  of  the  Third  Class.  —  When  the  body  lying  on 
the  ground  is  raised  to  a  sitting  posture,  a  lever  of  the 
third  class  is  used.  The  head  and  body  are  the  weight, 
the  fulcrum  is  at  the  hip  joints,  and  the  power  is  applied 


THE    MUSCULAR    SYSTEM 


69 


■^ 


between  the  two  by  the  mnseles  which  pass  from  the  front 
of  tlie  thigh  to  the  hip  bones.  The  raising  of  the  hand  by 
bending  tlie  elbow  joint  is  perhaps  a  clearer  example  of 
the  lever  of  the  third  class.  The  weight  is  at  the  end  of 
the  forearm,  the  fulcrum  is  at  the  elbow, 
and  the  power  is  between,  at  the  point 
on  the  radius  where  is  inserted  the  muscle 
which  lies  on  the  front  of  the  humerus. 

88.  Coordination  of  Muscular  Action. — 
Our  ordinary  movements  involve  the  use 
of  many  different  muscles,  and  very  com- 
plicated action  of  levers  and  cords.  Even 
simply  to  stand  erect  requires  strong  ten- 
sion of  certain  muscles  and  ligaments 
pulling  against  one  another.  The  mus- 
cles on  the  front  of  the  thigh  contract  to 
keep  the  knee  from  bending,  while  the 
ligaments  of  the  joint  prevent  it  from 
bending  tlie  wrong  way.  The  muscles 
on  the  front  of  the  leg  contract  to  keep 
the  body  from  falling  backward,  and  those 
at  the  back  contract  to  keep  it  from  fall- 
ing forward.  In  the  same  way  the  trunk 
is  balanced  on  the  thioii  bones  bv  the 
muscles   passing   from    the   body   to    the 

while  a  particu- 
ligament,  crossing  the  hip 
joint  from  the  pelvis  to  the  thigh  bone, 
keeps  the  extra  backward  weight  of  the 
trunk  from  destroying  the  balance  of  the  frame.  At  the 
back  of  the  neck  are  the  muscles  which  give  to  the  head 
its  erect  and  graceful  poise,  while  many  ligaments  bind  it 
to  the  spinal  column  (Fig.  46). 


thio'h  in  front  and  bac 
larly    strong 


Fig.  46.  — Diagram 
of  some  of  the 
muscles  which 
tend  to  keep  the 
body  erect. 


70  CONSCIOUS   NERVOUS   OPERATIONS 

89.  In  order  to  maintain  all  the  nice  adjustment  and 
balance  of  muscular  force  constantly  demanded,  the  brain 
and  nerves  must  be  continually  at  work.  Just  enough 
stimulus  must  be  supplied  to  each  set  of  muscles  and 
supplied  at  exactly  the  right  moment  or  something 
will  at  once  go  wrong.  This  harmony  of  muscular  ac- 
tion and  regulation  of  the  complex  relations  between 
the  hundreds  of  muscles  in  the  body  is  called  coor- 
dination. It  is  easy  to  show  that  it  depends  upon  the 
nervous  system. 

If  one  falls  asleep  or  receives  a  blow  which  "  stuns  " 
the  brain,  the  muscles  are  relaxed,  and,  unless  supported, 
the  body  falls  to  the  ground.  Sudden  nervous  or  emo- 
tional excitement,  as  surprise,  grief,  or  fear,  may  cause 
the  muscles  of  the  heart  to  stop  their  action  and  the  body 
to  fall  in  a  "  faint."  In  some  cases  the  effect  of  sight 
upon  the  brain  is  to  destroy  the  power  to  control  the 
muscles,  as  when  the  sight  of  the  moving  waves  of  lake 
or  ocean  renders  one  giddy.  The  perception  of  certain 
odors  may  have  the  same  effect,  and  in  many  other  ways 
the  control  of  the  muscles  is  affected  by  that  which  affects 
the  central  nervous  system. 

The  study  of  the  brain  has  shown  that  the  cerebellum 
is  the  great  center  for  the  coordination  of  muscular  move- 
ment and  especially  of  those  muscular  actions  which  have 
to  do  with  maintaining  the  equilibrium  of  the  body. 

90.  Exhaustion  of  Muscles.  —  Even  when  we  are  quite 
awake,  and  the  brain  is  active,  our  muscles  sometimes  refuse 
to  act.  Muscular  fiber  cannot  contract  continuously  for  a 
long  time.  It  must  have  periods  of  rest.  That  is  the 
reason  we  require  frequent  changes  of  position,  one  set 
of  muscles  being  thus  allowed  to  rest  while  another  set 
is  called  into  action.     If  a  weight  be  held  out  at  arm's 


THE   MUSCULAR   SYSTEM 


71 


length  from  the  shoulder,  the  muscles  of  the  arm  soon 
become  exhausted  and  incapable  of  sustaining  the  weight. 
But  a  moment's  rest  restores  the  contractile  power,  and 
the  weight  may  again  be  held 
out. 

91 .  Muscle  Waste.  —  When  a 
muscle  contracts  certain  chem- 
ical changes  take  place  in  the 
substance  of  its  cells.  Some 
of  the  matter  in  the  muscular 
fiber  becomes  oxidized,  and 
new  substances  are  formed 
which  are  harmful  to  the  body 
if  not  removed.  These  are 
called  waste  products^  and  that 
which  appears  in  largest  quan- 
tity is  carbon  dioxide.  These 
waste  products  are  taken  up 
by  the  blood  wliich  flows  along 
the  muscle  cells  and  are  finally 
removed  from  the  bod}^  by 
means,  mainly,  of  the  lungs 
and  the  kidneys.  If  the  waste 
matter  is  not  removed,  the 
effect  soon  appears  in  the  cen- 
tral nervous  system,  to  which 
the  poison  is  carried  by  the 
blood. 

92.  Voluntary  Movement.  — 
Let  us  suppose  that  a  man 
seeing  an  apple  within  reach  puts  forth  his  hand  to  take 
it  (Fig.  47).  In  such  a  case  the  light  from  the  apple 
enters  the  organ  of  sight  and  stimulates  the  nerve  endings 


Fig.  47.  —  Diagram  of  the  path  of 
a  nervous  impulse  which  re- 
sults in  the  hand  reaching  to 
seize  an  object  seen  with  the 
eye. 

C      cerebrum. 

Ch    cerebellum. 

M     medulla  oblongata. 

MC  motor  center  in  brain. 

OC  optic  center  in  brain. 

P      pons  Varolii. 

Q      corpora  quadrigemina. 

S      spinal  cord. 

T      optic  thalami. 


72 


CONSCIOUS  NERVOUS   OPERATIONS 


appropriated  .to  vision.  The  nervous  irritation  is  con- 
ducted by  the  optic  nerve  to  that  part  of  the  brain  con- 
cerned in  perception  by  means  of  the  eye.  Tlie  nervous 
center  is  affected,  and  the  nervous  impulse  is  passed  on, 
by  some  unknown  process  which  we  speak  of  as  the  action 
of  the  will,  to  the  nerve  fibers  running  down  the  white 
columns  of  the  spinal  cord.  These  convey  the  impression 
to  the  anterior  horn  of  the  gray  matter  of  the  cord,  where 
lie  the  motor  cells  from  which  arise  the  motor  roots  of  the 
spinal  nerves.  From  the  motor  cells  a  new  nervous 
impulse  goes  forth  to  certain  muscles  of  the  arm  and 
hand.  The  muscular  cells  of  such  muscles  contract,  the 
bones  are  moved  at  the  joints,  and  the  apple  is  seized. 
This  is  voluntary  muscular  action. 

93.   Reflex  Movement.  —  The  voluntary  muscles  often  act 
without  receiving  any  nervous  impulse   from   the  brain, 


Fig.  48  —Diagram  of  the  path  of  a  simple  nervous  reflex  action. 


and  without  any  conscious  purpose.  Suppose  the  man  in 
putting  out  his  hand  to  take  the  apple  is  stung  upon  the 
finger  by  a  wasp  not  before  perceived.  The  end  organ 
of  sensation  in  the   finger  sends  the  impression  of   pain 


THE   MUSCULAR   SYSTEM  73 

along  the  afferent  sensory  nerve  through  the  posterior  nerve 
root  to  the  cells  of  the  spinal  cord,  and  an  impulse  is  at 
once  sent  forth  along  efferent  motor  fibers  to  the  muscles 
of  the  hand  and  arm,  which  promptly  jerk  the  hand  away 
(Fig.  48). 

A  great  multitude  of  reflex  actions  are  possible  to  the 
muscles,  and  one  of  the  chief  functions  of  the  spinal  cord 
is  to  act  as  a  center  of  reflex  action. 

94.  Automatic  Movement.  —  Action  of  the  muscles  often 
occurs  without  any  obvious  stimulation  of  the  nerves  from 
Avithout.  That  is,  the  nervous  impulse  may  apparently 
arise  in  the  nerve  center  itself,  and  efferent^  or  outgoing 
influences  are  not  preceded  by  afferent^  or  incoming  influ- 
ences. Such  changes  often  occur  i^hythmieally  —  activity 
and  rest,  or  diminished  activity,  following  each  other  in 
regular  alternation  —  as  in  the  movement  of  the  muscles 
of  respiration ;  and  this  characteristic  is  believed  to  be 
due  to  certain  rhythmic  changes  which  take  place  in  some 
of  the  nervous  material  of  the  medulla  oblongata. 

95.  The  Muscular  Sense.  —  It  is  not  motor  nerve  fibers 
only  that  are  distributed  to  the  muscles ;  the  muscles 
receive  sensory  fibers  also  which  pass  to  the  posterior 
roots  of  the  spinal  nerves  and  convey  imj)ressions  from 
the  muscles  to  the  spinal  cord  and  thence  to  the  brain. 
These  impressions  are  called  the  muscular  sense.  They 
assist  our  judgments  of  weight,  and  inform  the  brain  of 
the  general  condition  of  the  muscles. 

96.  Hygiene  of  the  Muscles.  —  Muscles  increase  in  size 
and  in  strength  by  appropriating  suitable  material  from 
the  food,  and  by  use.  If  ill  fed  and  inactive,  they 
become  small  and  weak.  If  one  limb  is  made  useless  from 
disease  or  injury,  —  as  when  a  bone  is  broken,  —  its 
muscles  shrink  and  grow  soft,  so  that  the  unused  limb 


74  CONSCIOUS  NERVOUS   OPERATIONS 

becomes  perceptibly  smaller,  and,  of  course,  weaker  than 
its  fellow. 

97.  Exercise  is  indispensable  to  health  of  muscles. 
Growing  children  need  much  active  exercise  for  develop- 
ing and  hardening  the  muscles,  and  all  healthy  children 
crave  it.  Nothing  is  better  than  running  and  walking  for 
joromoting  the  growth  of  the  muscles,  for  developing  the 
power  of  the  lungs  and  the  heart,  and  so  for  aiding  both 
the  free  circulation  of  the  blood  and  its  purification,  by 
means  of  which  the  nutrition  of  the  whole  body  is  stimu- 
lated. Those  who  exercise  much  in  the  open  air  (which 
is  always  best)  have,  as  a  rule,  good  appetites,  for  food 
is  needed  to  repair  the  waste  caused  by  the  exercise. 

Many  diseases  are  prevented,  and  some  are  cured,  by 
suitable  exercise.  A  brisk  walk  of  several  miles  taken 
regularly  every  day  would  alone  do  much  to  keep  the 
whole  body  in  normal  condition.  If  it  is  impossible  to 
go  out  of  doors  for  the  needful  amount  of  exercise,  the 
indoor  conditions  should  be  as  nearly  as  possible  like 
those  without.  Fresh  air  and  light  should  be  freely 
admitted  to  the  rooms  used,  additional  clothing  being 
put  on  when  necessary. 

Rowing,  swimming,  boxing,  horseback  riding,  climbing, 
sweeping,  cycling,  etc.  are  of  value  in  strengthening  the 
muscles  of  the  limbs,  chest,  and  back.  A  large,  strong 
chest,  wherein  the  lungs  have  plenty  of  room  for  an  abun- 
dance of  pure  air,  is  not  likely  to  belong  to  a  consumptive 
person. 

It  is  desirable  that  exercise  should  be  chosen  which 
develops  both  sides  of  the  body.  Throwing  a  ball  with 
one  hand,  if  indulged  in  to  excess  or  without  sufficient 
exercise  of  other  sorts,  sometimes  causes  irregular  devel- 
opment of  the  body,  and  curvature  of  the  spine  may  fol- 


THE   MUSCULAR   SYSTEM  75 

low.       Certain  kinds  of   spinal  curvature  are  cured  by 
wisely  chosen  exercise. 

98.  Exercise  in  the  Cold.  —  For  a  healthy  person  nothing* 
so  well  develops  tlie  whole  system  and  hardens  the  con- 
stitution as  regular,  vigorous,  and  agreeable  exercise  in  the 
cold.  Hence  outdoor  winter  sports  and  occupations 
should  be  encouraged.  Skating,  sliding,  snowballing, 
and  swimming  are  excellent  as  promoters  of  health. 

99.  Time  for  Exercise.  —  Some  times  are  better  than 
others  for  taking  exercise.  The  morning  is  usually  best 
for  the  severer  forms,  because  the  whole  system  is  then 
refreshed  and  vigorous.  In  the  evening  one  who  has 
been  engaged  in  physical  toil  does  not  need  exercise,  but 
rest  ;  while  one  whose  occupation  is  mental  labor  or  sed- 
entary business  will  be  rested  and  refreshed  and  prepared 
for  sound  sleep  by  exercising  judiciously  in  the  ojDen  air 
after  the  day's  work  is  done. 

When  the  muscles  are  called  into  use  they  require  more 
blood  than  when  at  rest,  that  the  waste  which  results 
from  exercise  may  be  repaired.  This  extra  supply  of 
blood  is  drawn  from  other  parts  of  the  body,  and  the 
demands  of  the  muscles  may  retard  the  performance  of 
other  physiological  functions  —  since  the  total  amount  of 
blood  is  practically  invariable.  This  is  why  the  muscles 
should  not  be  vigorously  exercised  for  an  hour  or  two,  at 
least,  after  meals,  and  not  immediately  before.  Digestion 
requires  an  increased  flow  of  blood  to  the  alimentary  canal 
and  digestive  glands,  and  if  the  process  is  impeded  by  a 
drain  of  the  vital  fluid  to  other  parts,  harm  Avill  result. 

100.  Training.  —  The  scientific  development  of  the  mus- 
cular system  under  ''  training  "  for  particular  purposes  of 
sport,  or  in  a  well-equipped  gymnasium,  may  have  excel- 
lent results  for  those  who  are  able  to  avail  tliemselves  of 


76  CONSCIOUS  NERVOUS   OPERATIONS 

sucli  facilities.  But  the  number  of  such  persons  is  com- 
paratively small,  and  as  those  who  exercise  in  a  gymna- 
sium are  usuall}^  and  ought  always  to  be,  under  the  guid- 
ance of  a  qualified  instructor,  advice  as  to  the  use  of  the 
gymnasium  apparatus  is  not  needed  here. 

101.  The  Healthfulness  of  Work. —While  all  due  stress 
should  be  laid  upon  the  healthfulness  of  recreative  exer- 
cise, it  should  not  be  forgotten  that  the  human  machine 
is  the  most  skillfully  designed  and  constructed  apparatus 
ever  made  for  accomplishing  an  immense  variety  of  differ- 
ent kinds  of  luork.  The  man  whose  daily  employment 
brings  into  play  his  various  muscles  under  conditions  of 
reasonable  comfort,  and  without  overfatigue,  may  live  a 
healthful  life  without  paying  any  attention  to  the  preced- 
ing suggestions.  If  that  employment  is  carried  on  in  the 
open  air,  and  is  such  that  he  finds  interest  and  enjoyment 
in  it,  he  is  still  more  fortunate.  All  the  good  effects  of 
the  most  carefully  devised  systems  of  physical  culture 
may  be  gained  from  a  judiciously  varied  scheme  of  work, 
and  the  pleasure  of  being  able  by  one's  own  effort  to 
create  some  useful  or  beautiful  or  worthy  product  for  the 
eimchment  of  the  world  may  be  a  tonic  even  more  health- 
fully stimulating  than  the  most  successful  athletic  con- 
test. The  varied  round  of  household  duties,  sometimes 
prescribed  by  a  wise  and  skillful  physician,  has  in  many 
cases  brought  health  to  a  feeble,  languid,  ailing  woman. 
The  effort  which  the  idle  rich  man  sometimes  puts  forth 
in  the  way  of  exercise,  tliat  he  may  secure  an  appetite  for 
his  dinner,  would  be  still  more  promotive  of  health  if 
turned  to  some  useful  purpose. 

The  man  whose  business  does  not  permit  the  proper 
activity  of  all  the  muscles  must  necessarily  give  thought 
and  time  to  supply  the  deficiency.     But  to  the  great  mass 


THE   MUSCULAR   SYSTEM  77 

of  mankind  it  is  happily  possible  to  get  all  needful  exer- 
cise while  doing  useful  work. 

102.  The  Nervous  System  as  involved  in  Muscular  Exercise. 
—  We  have  already  learned  that  contraction  of  voluntary 
muscular  tissue  depends  upon  the  stimulus  brought  to 
each  minute  muscle  cell  by  a  nerve  fiber.  Without  such 
stimulus  a  man's  limbs  are  motionless  and  the  whole  frame 
a  lifeless  mass.  If  the  nervous  system  is  enfeebled  by 
disease  or  by  exhaustion,  the  action  of  the  muscles  becomes 
weakened  or  deranged.  The  disease  called  Saint  Vitus's 
danee,  which  causes  muscular  movements  beyond  the  con- 
trol of  the  will,  is  not  a  disease  of  the  muscles,  but  of  the 
nerves.  So  in  other  disorders  which  derange  the  action 
of  the  muscles,  the  real  trouble  is  seldom  with  the  muscu- 
lar tissue  itself.  The  direct  effect  of  muscular  activity, 
as  suggested  in  section  91,  is  to  poison  the  nervous  cen- 
ters. The  greater  the  demand  upon  the  muscle  in  the 
way  of  rapid  and  frequent  contraction,  the  greater  the  con- 
sumption of  living  material  and  the  greater  the  amount  of 
poisonous,  dead,  waste  matter  which  passes  into  the  circu- 
lation. These  waste  products,  if  not  promptly  removed 
from  the  system  through  the  excretory  organs,  are  found 
to  have  a  powerful  injurious  effect  upon  the  central  nerv- 
ous system,  an  effect  that  is  soon  manifest  in  the  weak- 
ened action  of  the  muscles  themselves. 

Anything,  therefore,  which  affects  injuriously  the  nerv- 
ous system  interferes  with  the  free  and  easy  play  of  the 
muscles.  And,  conversely,  anything  which  promotes  a 
high  level  of  health  in  the  nervous  system  is  an  aid  to  mus- 
cular vigor  also.  Exercise  undertaken  for  the  carrying 
out  of  some  worthy  purpose  —  a  purpose  in  which  the 
mind  is  deeply  interested  and  the  whole  man  engaged  — 
is  the  most  healthful  exercise  ;  while  that  which  is  disliked 


78  CONSCIOUS  NERVOUS   OPEEATIONS 

or  entered  upon  indifferently  and  listlessly  is  found  to 
have  little  or  no  invigorating  power. 

103.  Effect  of  Alcohol  and  Other  Stimulants  and  Narcotics 
upon  Muscular  Action.  —  The  most  serious  effects  of  the 
excessive  use  of  alcoholic  drinks,  tobacco,  opium,  chloral, 
and  other  narcotic  drugs  are  felt  b}'  the  nervous  system 
and  will  be  most  fully  treated  when  we  come  to  the  special 
study  of  that  part  of  the  human  organism.  But  it  is  well 
to  notice  here  how  those  substances  influence  the  organs 
of  motion. 

No  one  who  has  ever  seen  a  drunken  man  in  the  stage  pre- 
ceding that  of  stupor  can  have  failed  to  observe  the  uncer- 
tainty of  his  muscular  movements  :  the  shaking  hand,  the 
staggering  gait,  the  thick,  indistinct  utterance.  These 
effects  are  due  to  what  is  called  the  excessive  use  of  alco- 
holic drinks,  and  no  one  doubts  that  in  large  quantities 
they  act  injuriously  upon  the  system.  Alcohol  deranges 
the  action  of  the  muscles  by  its  influence  upon  the  nervous 
system,  causing  defective  regulation  of  the  supply  of  nerv- 
ous force  to  the  several  muscles.  As  to  whether  it  is  pos- 
sible to  use  alcohol  in  small  amounts  without  impairing 
the  perfection  and  vigor  of  muscular  action,  there  is  one 
very  significant  fact :  that  men  in  training  for  severe  mus- 
cular exertion  in  athletic  contests  are  strictly  forbidden 
the  use  of  alcohol  in  any  form  and  in  any  quantity, 
whether  or  not  they  have  been  previously  accustomed  to 
such  indulgence.  As  the  rules  for  such  training  are  the 
result  of  long  and  wide  experience  and  most  careful  study, 
it  is  safe  to  conclude  that  alcohol  at  least  does  not  promote 
strength,  endurance,  or  precision  of  muscular  movement. 

It  is  very  common  for  a  person  accustomed  to  a  moder- 
ate use  of  alcoholic  beverages  to  suffer  from  tremor  of  the 
hands,  due  to  lack  of  control   over  the  muscles,  so  that 


THE    MUSCULAR   SYSTEM  79 

he  is  disabled  from  manual  work  requiring  dexterity  or 
skill.  Sometimes  an  additional  glass  of  liquor  seems 
to  steady  the  hand  for  a  time,  but  tne  shakiness  soon 
returns. 

104.  Tobacco  and  other  narcotics  also  affect  muscular 
activity  through  their  effect  upon  the  nerves.  All  nar- 
cotics have  as  their  natural,  characteristic  influence  the 
paralyzing  of  some  of  the  nerve  centers.  As  medicines 
they  may  give  relief  from  pain  and  so  act  beneficently 
under  skillful  application.  Tobacco  has  a  special  effect 
upon  the  nerve  centers  regulating  the  action  of  the 
muscles  of  the  heart,  making  that  action  irregular  and 
less  vigorous.  This  is  particularly  true  of  the  young,  and 
it  is  not  very  uncommon  for  boys  addicted  to  excessive 
cigarette  smoking  to  develop  serious  disease  of  the  heart, 
or  even  to  die  suddenly  from  "  heart  failure."  Smoking 
tobacco  is  found  to  interfere  with  work  requiring  fine  and 
delicate  adjustment  of  muscular  movement,  as  in  watch 
making  and  other  delicate  mechanical  employments,  in 
scientific  drawing,  fine  penmanship,  etc.  It  is  also  for- 
bidden to  those  persons  in  training  for  athletic  contests, 
and  to  all  pupils  in  many  schools,  as  well  as  to  soldiers  in 
the  armies  of  certain  countries. 

Demonsteattons  and  Experiments 

17.  General  Structure  and  Properties  of  Muscles.  —  It  is  important 
that  the  pupils  see  muscles  in  their  natural  positions  and  connections. 
For  this  purpose  the  frog  is  convenient,  since  the  animal  is  so  small 
that  little  dissection  is  necessary,  and  since  entire  muscles  can  be 
observed  and  owing  to  their  great  vitality  can  be  made  to  perform 
their  natural  movements.  The  frog  should  be  pithed  or  decapitated, 
and  the  skin  removed  from  one  of  the  hind  legs.  The  muscles  of 
the  limb  then  stand  out  distinctly  (Fig.  7,  p.  18).  The  belly  of  a 
muscle  can  be  distinguished  from  its  tendinous  ends,  and  the  origin 


80  CONSCIOUS   NERVOUS   OPERATIONS 

and  the  insertion  can  be  made  out.  The  respective  share  wnich  each 
muscle  takes  in  the  movements  of  the  limb  can  be  shown  by  touch- 
ing the  individual  muscles  with  the  electrodes  of  a  weak  galvanic 
battery.  The  change  in  shape  of  the  muscle  during  contraction  will 
also  be  very  well  shown. 

18.  Relaxation  and  Contraction  q/ il/wscZes.  —  Extend  one  arm  nearly 
straight  from  the  shoulder.  Then  bend  the  arm  at  the  elbow,  draw- 
ing the  hand  up  to  the  shoulder.  With  the  other  hand  can  be  felt 
the  changes  in  the  form  of  the  biceps  muscle,  as  it  relaxes  and  con- 
tracts. If  the  arm  be  bared  the  changes  in  form  of  the  muscle  can 
be  seen.     The  tendon  of  the  biceps  at  the  elbow  can  also  be  seen. 

19.  Gross  Structure  of  Muscle.  —  Obtain  a  piece  of  boiled  corned 
beef,  and  dissect  it  with  needles.  The  larger  and  smaller  bundles  of 
muscle  fibers  can  be  easily  differentiated.  By  aid  of  a  lens  even  the 
separate  fibers  can  be  isolated.  Observe  between  the  bundles  and 
fibers  the  whitish  connective  tissue,  in  life  tough  and  fastening  the 
bundles  and  fibers  together,  but  now  softened  in  boiling. 

20.  Functional  Difference  hetiveen  Voluntary  and  Involuntary  Muscle. 
—  If  the  abdominal  cavity  of  the  frog  experimented  upon  in  a  preced- 
ing section  be  opened  and  the  electrodes  applied  to  the  stomach  and 
intestines,  the  difference  between  the  movements  of  vohmtary  and 
involuntary  muscle  will  be  clearly  demonstrated. 

21.  Fatigue  of  Muscle.  —  On  applying  repeated  electric  shocks 
directly  to  a  frog's  muscle,  or  indirectly  through  its  nerve,  the  re- 
sponses are  seen  to  become  more  and  more  feeble.  But  after  a  period 
of  rest,  the  muscle  responds  as  vigorously  as  ever. 

22.  Nerve  Endings  in  Muscle.  —  While  the  tracing  out  of  the  final 
nerve  ends  in  muscle  must  be  left  to  the  histological  expert,  yet 
the  general  relations  of  motor  nerves  to  muscles  can  be  very  easily 
shown  in  the  frog.  Branches  of  the  sciatic  nerve  can  be  traced  out 
to  the  muscles  of  the  leg  (Fig.  8,  p.  18),  and  by  electrical  stimulation 
the  functional  relation  between  nerve  and  nmscle  can  be  shown. 

23.  Rigor  Mortis.  —  Observe  in  a  frog,  just  after  decapitation,  that 
the  muscles  are  soft  and  relaxed.  Shortly  after  the  tissues  have  com- 
pletely lost  their  vitality,  the  muscles  will  be  found  to  be  hard  and 
contracted.  The  limbs  which  may  have  been  bent  at  the  joints  and 
limp,  are  now  straight  and  rigid.  Death  rigor  or  7-igor  mortis  has  set 
in.  After  some  time,  the  muscles  again  become  flaccid  and  putrefac- 
tion soon  begins.     Place  fresh  muscle  in  hot  water,  and  observe  that 


THE    MUSCULAR   SYSTEM  81 

heat  rigor  is  at  once  manifest.     In  both  cases,  the  rigor  is  due  to 
coagulation  of  the  muscle  substance. 

24.  Minute  Structure  of  Voiuntury  or  Striped  Muscle.  —  With  needles 
tease  out,  in  normal  salt  solution,  on  a  glass,  a  small  piece  of  skeletal 
muscle  of  a  frog  or  other  animal.  Mount  and  examine  with  the  com- 
pound microscope.  It  will  be  seen  to  be  composed  of  elongate  thread- 
like bodies,  tapering  (when  not  broken)  at  the  ends.  Some  fibers  will 
show  cross  markings. 

25.  The  Minute  Structure  of  Involuntary  or  Plain  Muscle. — Tease 
out,  as  in  the  foregoing,  a  small  piece  of  the  outer  wall  of  the  intestine 
of  a  frog  or  cat.  Here  the  fibers  are  seen  to  be  spindle-shaped  cells, 
nmch  shorter  than  the  striped  muscle  fibers. 

The  fibers  of  both  striped  and  plain  muscle  can  be  much  more 
easily  teased  apart  if  the  tissue  be  kept  in  a  20  per  cent  solution  of 
nitric  acid  one  to  two  days. 

26.  Cross  Section  of  Muscle.  Minute  Structure.  —  If  a  prepared 
cross  section  of  a  small  skeletal  muscle  can  be  obtained,  the  internal 
structure  of  a  muscle  can  be  very  well  shown  by  aid  of  the  compound 
microscope. 

27.  Minute  Structure  of  Tendon  and  Ligament.  —  Carefully  tease 
out  in  normal  salt  solution,  on  a  slide,  a  small  piece  of  a  thin  tendon 
from  the  tail  of  a  mouse.  To  obtain  the  tendon,  cut  off  the  tail  from 
the  body,  and  then  pull  out  the  delicate  tendinous  threads  from  the 
cut  end.  The  tendon  should  be  mounted  immediately  after  removal, 
to  avoid  drying.  A  convenient  method  of  mounting  is  to  stretch  the 
tendon  across  a  slide,  through  a  drop  of  normal  salt  solution  in  the 
center,  allowing  the  ends  of  the  tendon  to  adhere  to  the  dry  edges  of 
the  slide.  On  examining  wdth  the  compound  microscope  the  tendon 
is  seen  to  be  composed  of  wavy  bundles  of  fibers.  If  the  preparation 
be  treated  with  a  one  per  cent  solution  of  acetic  acid,  the  fibers  will 
swell  and  disappear  from  view,  but  there  will  appear,  between  the 
bundles,  rows  of  spindle-shaped  cells. 


MACY'S    PHYS. 


CHAPTER  VI 

THE  SKIN  AS  AN  ORGAN  OF  SENS ATION  —  TOUCH 

105.  Functions  of  the  Skin.  —  The  whole  body  is  covered 
with  a  flexible,  elastic  membrane  of  complex  structure, 
which  serves  several  different  purposes.  It  envelops 
and  protects  the  inner,  soft  parts,  and  especially  the  ends 
of  the  nerves.  It  is  one  of  the  three  principal  channels 
by  which  the  waste  products  of  the  body  are  removed 
—  that  is,  it  is  an  organ  of  excretion.  It  regulates  the 
temperature  of  the  body  by  controlling  the  loss  of  heat 
through  general  radiation  and  evaporation,  as  well 'as  by 
the  direct  action  of  the  sweat  glands  in  excretion.  A 
small  amount  of  respiration,  or  exchange  of  gases,  also 
goes  on  in  the  skin,  and  it  contributes  by  its  general  char- 
acteristics and  its  various  modifications  to  the  ornamen- 
tation of  the  body. 

106.  Structure  of  the  Skin.  —  The  present  chapter  has  to 
do  with  the  skin  as  one  of  the  organs  by  means  of  which 
the  nervous  S3^stem  is  brought  into  direct  communication 
with  the  external  world,  that  is,  as  the  seat  of  the  sense 
of  touch  and  of  certain  other  allied  nervous  impressions. 

Two  distinct  layers  are  found  in  the  skin,  called  the 
epidermis^  or  cuticle^  and  the  dermis^  corium^  or  true  skin 
(Fig.  49).  The  epidermis  is  composed  of  epithelial  tis- 
sue, or  epithelium,  and  its  cells  lie  in  layers  one  above 
another,    the    outer    or  horny    layer    of    cells    being  flat, 

82 


THE   SKIN   AS   AN   ORGAN   OF   SENSATION 


83 


dry,  and  unnucleated,  or  dead.  The  epidermis  contains 
no  blood  vessels,  but  in  the  deepest  layers  are  found 
minute  terminations  of  some  of  the  nerve  fibers;  and  in 
the  same  layers  are  the  fine  granules  called  pigment  which 
give  color  to  the  skin.  This  coloring  matter  is  power- 
fully affected  b}'  sun  and  wind,  causing  tan  and  freckles. 


Horny  layer  <^  ^ 
Pigment  layer 


Tactile  Organ 

Nerve" 

Blood  Vessels- 

Sweat  Gland- 


Epidermis 


>  Dermis 


Fig.  49.— Diagram  of  section  of  the  skin. 

107.  Hair  and  Nails  are  peculiarly  developed  forms  of 
the  cuticle.  Each  hair  is  a  long  filament  growing  obliquely 
from  a  little  bulb  called  a  papilla,  lying  in  a  hollow  called 
the  hair  follicle,  Avhicli  reaches  down  below  the  skin  into 
the  areolar  tissue  beneath  (Fig.  49).  The  part  of  a  hair 
buried  in  the  skin  is  called  its  root;  the  remainder,  the 
stem,  which  tapers  to  a  point.  The  stem  is  covered  with 
scales  overlapping  like  the  scales  of  a  fish  and  project- 
ing toward  the  point.  When  a  hair  is  pulled  out  by  the 
root,  a  new  one  will  grow  again  so  long  as  the  papilla  is 
uninjured.     Each  hair  contains  pigment  granules  which 


84  CONSCIOUS   NERVOUS   OPERATIONS 

give  its  color.  There  are  also  cavities  filled  with  air. 
These  small  bodies  of  inclosed  air  are  very  abundant  in 
white  hair,  and,  reflecting  the  light,  are  the  cause  of  its 
color,  just  as  the  whiteness  of  snow  is  due  to  the  many 
reflections  of  light  from  the  tiny  bits  of  ice  which  compose 
it. 

In  the  nails  the  horny  layer  of  the  epidermis  is  greatly 
developed.  Each  nail  has  its  root  firmly  embedded  in  a 
groove  of  the  cuticle.  The  under  side  is  fixed  to  the  der- 
mis except  at  the  end  of  the  linger  or  toe,  where  there  is 
a  free  edge. 

The  hair  preserves  the  temperature  of  the  head  and 
is  also  a  protection  against  injury.  The  nails  protect 
the  sensitive  ends  of  fingers  and  toes  and  aid  in  their 
mechanical  operations.  Both  hair  and  nails  also  help  in 
the  ornamentation  of  the  body. 

108.  Mucous  Membrane. — Not  only  is  the  whole  outer 
surface  of  the  body  covered  with  the  skin,  but  all  the 
inner  cavities  and  passages  which  have  an  external  com- 
munication are  also  lined  with  it.  These  inner  linings 
are,  however,  of  a  modified  form  of  skin  called  mucous 
membrane^  because  it  secretes  a  viscous  fluid,  or  mucus. 
This  membrane  is  thinner,  redder,  and  more  sensitive  and 
delicate  than  the  outer  skin,  but  is  of  the  same  general 
composition  ;  that  is,  it  has  the  two  layers,  the  outer 
bloodless  and  insensible,  the  inner  highly  sensitive,  soft, 
fully  supplied  with  blood  vessels,  glands,  etc. 

109.  The  Dermis,  or  True  Skin,  is  a  close  network  of 
connective  tissue  fibers,  forming  a  dense,  tough,  firm 
envelope  for  the  body,  resting  upon  and  gradually  pass- 
ing into  the  areolar  tissue  beneath,  which  is  a  loose 
network  of  interlacing  bands  and  cords  with  meshes 
between.       Ramifying    through   the   dermis   are   nerves, 


THE   SKIN   AS   AN   ORGAN  OF   SENSATION  85 

blood  vessels,  and  lymphatic  vessels,  and  it  contains  great 
numbers  of  sweat  glands  and  oil  glands. 

The  epidermis,  lacking  blood  vessels,  does  not  bleed, 
and  the  horny  layer,  lacking  nerves,  has  no  feeling;  but  so 
fine  are  the  networks  of  blood  vessels  and  nerves  in  the 
dermis  that  the  finest  needle  cannot  pass  between  them. 
The  whole  surface  of  the  dermis  is  thrown  into  innumer- 
able projections  called  papillce,  many  of  them  supplied 
with  capillary  blood  vessels  and  nerve  fibers. 

110.  Sensation. — When  we  become  conscious  of  receiv- 
ing an  impression, —  that  is,  when  we  perceive  that  some 
part  of  our  nervous  system  is  stimulated,  —  we  have  what 
is  called  sensation.  It  has  already  been  shown  that  nerv- 
ous stimulation  may  affect  parts  of  the  nervous  system 
and  reflex  action  may  follow  without  conscious  reception 
by  the  brain  of  any  influence  —  that  is,  without  sensation. 

In  order  that  there  may  be  sensation  there  must  be  (1) 
a  stimulus.,  (2)  a  nervous  end  organ  suited  to  receive  the 
stimulus,  (3)  a  path  to  the  brain  for  the  impulse  excited  by 
the  stimulus,  (4)  a  part  of  the  brain  to  receive  the  impulse. 
Still  another  condition  of  a  different  sort  seems  essential 
to  sensation,  and  that  is  an  attitude  of  the  mind  which 
we  call  attentio7i.  A  person  absorbed  in  thought  may  look 
upon  an  object  without  being  conscious  of  perceiving  it, 
may  hear  music  without  knowing  it.  That  is,  all  the  con- 
ditions of  sight  and  hearing  may  be  present  save  the  one 
of  attention,  for  Avhich  we  have  as  yet  no  physiologically 
descriptive  terms. 

111.  General  and  Special  Sensations.  —  There  are  various 
vague,  indefinable  feelings  which  are  not  referred  to  any 
particular  portion  of  the  body  or  to  any  external  influence, 
and  which  we  know  as  general  sensibility .  Sensations  of 
fatigue,  of  restlessness,  languor,  weakness,  and  the  like, 


86  CONSCIOUS   NERVOUS   OPERATIONS 

are  of  this  sort.  It  is  supposed  that  these  are  associated 
with  the  ramifying,  interlacing  plexuses  of  nerve  fibrils  in 
many  parts  of  the  body,  and  are  not  due  to  the  excitation 
of  specially  constructed  nerve  endings. 

Other  sensations  are  more  definite.  We  judge  them  to 
be  caused  by  some  influence  acting  upon  particular  parts 
of  the  body.  What  have  long  been  known  as  the  jive 
senses  are  of  this  sort.  But  we  now  recognize,  in  addi- 
tion to  touch,  taste,  smell,  sight,  and  hearing,  other  sensa- 
tions apparently  distinct  from  them,  for  which,  in  some 
cases  at  least,  special  nerve  endings  are  provided,  and  spe- 
cial brain  centers.  These  are  sensations  of  temperature, 
of  pain,  of  hunger,  and  of  thirst,  and  the  muscular  sensa- 
tions previously  mentioned  (§  95). 

112.  The  Sense  of  Touch.  —  Touch  has  been  defined  as  a 
sense  of  pressure  referred  to  the  surface  of  the  body.  It  is 
that  sort  of  impression  upon  the  nervous  system  which 
gives  information  respecting  certain  properties  of  bodies 
in  contact  with  the  skin  or  mucous  membrane.  Through 
it  we  learn  whether  an  object  is  hard  or  soft,  rough  or 
smooth,  and  other  particulars,  some  of  which  are  also  given 
by  the  sense  of  sight. 

The  skin  is  supplied  with  a  variety  of  special  adapta- 
tions which  constitute  it  the  orga^i  of  touch. 

113.  The  Nervous  Apparatus  for  Touch. — The  thirty-one 
pairs  of  spinal  nerves  contain  the  fibers  for  feeling  for 
the  larger  part  of  the  body,  as  well  as  most  of  the  motor 
nerve  fibers  supplying  the  muscles.  It  will  be  remem- 
bered that  each  spinal  nerve  arises  by  two  roots  from  the 
spinal  cord,  one  root  containing  afferent  or  sensory  fibers, 
the  other  efferent  or  motor  fibers.  By  the  union  of  the 
two  roots  the  nerve  is  formed,  which  thence  contains  both 
sorts  of  nerve  fibers,  as  do  its  large  branches. 


THE   SKIN   AS    AN   ORGAN   OF   SENSATION 


87 


114.  In  the  neck,  loins,  and  pelvis  adjacent  nerves 
interlace  with  one  another  to  form  a  plexus^  or  network. 
In  a  plexus  nerve  fibers  from  two  or  more  nerves  are 
brought  into  connection  in  such  a  way  that  the  parts  of 
the  body  which  receive  nervous  fibers  from  the  plexus 
have  communication  with  a  greater  number  of  nerve  trunks 
and  nerve  centers,  and  may  receive  more  complex  im- 
pulses, than  do  those  parts  to  which  branches  go  from 
but  a  single  nerve  trunk.  This  is  why  these  plexuses 
are  so  frequently  found  in  connection  with  the  nerves 
going  to  the  limbs,  where  great  complexity  of  motion  and 
careful  coordination  are  required. 

The  nerves  of  the  skin  form  plexuses  in  the  dermis. 
In  some  parts  of  the  body  these  contain  fibers  from  spinal 
nerves  and  also  from  certain  of  the  cranial  nerves.  From 
these  plexuses  minute  nerve  fibers  pass  to  the  papilkne, 
which  contain  the  tactile  end  organs. 

115.  Tactile  End  Organs.  —  End  orgmis  are  those  pecul- 
iarly formed  nerve  cells  or  groups  of  cells  which  receive 
and  pass  on  the  stimulus  to  which 
they  are  adapted.  Tactile  end  organs 
are  of  several  different  forms. 

Pacinian  corpuscles  are  found  deep 
in  the  dermis,  scattered  along  the  line 
nerve  branches  like  buds  on  a  plant. 
Each  corpuscle  consists  of  layers  of 
delicate  membrane  within  which  is  a 
single  minute  nerve  fiber  (Fig.  50). 
Another  form  of  end  organ,  called  the 
touch  corpuscle^  appears  especially  in 
the  papillae  of  fingers  and  toes,  and  is 
much  smaller  than  the  Pacinian  corpuscle.  The  touch 
corpuscles  are  oblong  masses,  each  containing  a  capsule 


e  Fiber 


Fig.  50.  — Pacinian 
corpuscle. 


88 


CONSCIOUS   NERVOUS   OPERATIONS 


Fig.  51.— Touch 
corpuscle  in  pa- 
pilla of  tlie  skin 
of  the  hand. 

C  touch  corpuscle. 

JSf  nerve  fibers 
■winding  around 
the  corpuscle. 


which  receives  a  nerve  whose  fibers  wind  round  and 
round  the  capsule  before  entering  it  (Fig.  51).  Still 
smaller  end  bulbs  are  found  in  the  skin, 
made  up  of  nerve  fibers  ending  in  corpus- 
cles in  which  the  axis  cylinder  of  the  nerve 
terminates.  All  the  tactile  end  organs  are 
covered  by  the  epidermis,  so  that  the  nerves 
themselves  are  not  brought  into  actual 
contact  with  the  external  thing  which  they 
feel.  If  the  cuticle  were  stripped  off  and 
pressure  applied  to  a  naked  nerve  end- 
ing, there  would  be,  not  a  sense  of  touch 
with  ability  to  judge  of  the  properties  of 
the  body  causing  the  sensation,  but  in- 
stead a  sense  of  pain.  Certain  portions 
of  the  skin  are  more  fully  supplied  with 
end  organs  for  touch  than  are  others,  and  the  epidermis 
there  is  thinner,  so  that  the  sense  of  touch  is  more  deli- 
cate. The  tip  of  the  tongue,  the  skin  of  the  face,  and 
the  ends  of  the  fingers  are  most  sensitive.  A  pair  of 
blunt-pointed  compasses  applied  to  the  end  of  the  tongue 
will  be  distinguished  as  two  j^oints  even  when  they  are 
separated  by  only  one  twenty-fourth  of  an  inch,  while 
they  would  be  felt  as  but  one  point  on  the  finger  ;  and 
on  the  arm  or  back  of  the  hand  the  two  points  much 
further  apart  would  seem  but  one. 

116.  Sensations  of  Heat  and  Cold. — Sensations  of  touch 
arise  from  pressure,  but  through  the  skin  we  have,  besides, 
sensations  of  heat  and  cold  ;  that  is,  we  perceive  changes 
of  temperature.  It  is  thought  that  experiments  indicate 
in  the  skin  a  separate  set  of  end  organs  stimulated  by 
heat,  and  another  set  which  is  stimulated  by  cold. 

117 >  The  Muscular  Sense.  —  Still  another  sensation  asso- 


THE   SKIN  AS   AN   ORGAN   OF   SENSATION  89 

ciated  Avitli  the  sense  of  touch  is  that  called  the  muscular 
sense  (^§95).  By  means  of  this  sense  we  judge  of  the 
weight  of  a  body.  When  we  hold  an  object  in  the  hand  we 
feel  its  pressure  upon  the  skin,  and  Ave  also  are  conscious 
of  a  muscular  effort  to  support  its  weight.  We  lift  it  up, 
move  it  from  place  to  place,  and  by  the  amount  of  effort 
put  forth  judge  of  the  Aveight  of  the  object.  In  this  pro- 
cess the  muscles  are  iuA^olved  as  Avell  as  the  cutaneous 
organs  of  sensation. 

Again,  Ave  are  conscious,  CA^en  Avith  our  eyes  closed,  of 
the  position  of  the  AA'hole  body.  (This  Ave  shall  find  to  be 
connected  with  a  certain  part  of  the  internal  ear,  §  179.) 
We  are  also  conscious  of  the  position  of  different  parts  of 
the  body  in  relation  to  one  another,  and  AAdien  Ave  come  in 
contact  Avith  external  objects  Ave  perceiA^e  not  only  the 
pressure  from  them  aft'ecting  our  organs  of  touch,  but 
also  the  pressure  AA'hich  Ave  exert  by  muscular  contrac- 
tion upon  them ;  that  is,  the  resistance  to  our  movements 
which  is  exerted  by  external  things.  It  is  sometimes 
said  that  Ave  haA'e  a  ''  sense  of  effort "'  (or  Aveight),  a 
''  sense  of  position,"  and  a  ''  sense  of  moA^ement,"  but 
all  these  are  included  in  the  more  general  term,  muscu- 
lar se7ise. 

118.  Pain.  —  It  is  not  yet  fully  determined  AAdiether  the 
sensation  Avhich  Ave  call  pain  is  due  merely  to  excessive 
stimulation  of  the  already  knoAvn  sensory  organs,  or  is  a 
distinct  sensation.  Sometimes  there  is  disease  of  sensory 
tracts  AA'hich  destroys  sensitiA^eness  to  pain,  though  the 
sense  of  touch  is  unaffected.  It  may  be  that  the  nerA^e 
fibers  already  referred  to,  AA'hich,  distributed  everywhere 
through  the  body,  constantly  convey  to  the  brain  impres- 
sions of  which  Ave  are  usually  hardly  conscious,  and  Avliich 
we  call  impressions  of  general  sensibility,  are  the  channels 


90 


CONSCIOUS  NERVOUS   OPERATIONS 


by  which  a  sense  of  pain  is  conveyed  when  they  are  more 
strongly  stimnlated. 

119.   Path  of  a  Touch  Impression.  —  Let  a  touch  corpuscle 
be  stimulated  by  pressure,  and  what  follows?     (Fig.  52.) 

The  cells  of  the  end 
organ  communicate 
the  impulse  to  the 
afferent  nerve  fibers 
passing  from  the 
touch  corpuscles  to 
the  nerve  distributed 
to  that  part  of  the 
skin.  The  sensory 
nerve  fibers  may  run 
through  more  than 
one  nerve  plexus  and 
through  ganglionic 
nerve  centers.  'There 
may  be  several  breaks 
in  the  path,  where 
the  original  impulse 
is  handed  over  from 
one  fiber  to  another, 
or  passes  from  cell 
to  cell,  or  from  fiber 
to  cell ;  but  the  im- 
pulse finally  reaches 
the  spinal  cord  (ex- 
cept when  a  cranial  nerve  conveys  the  impulse),  through 
a  posterior  nerve  root^  and  the  cells  of  the  gray  matter  of 
the  cord  are  stimulated. 

But  there  is  yet  no  sensation,  even  though  by  the  reflex 
action  of  the  cord  a  motor  impulse  may  be  sent  out  by  an 


Fig.  52. —Diagram  of  the  path  of  a  touch 
impression. 

The  dotted  lines  show  the  path  when  the  im- 
pulse ascends  to  the  brain,  exciting  conscious- 
ness, and  through  the  motor  center  {MC), 
producing  voluntary  motion. 


THE   SKIN   AS   AN   OKGAN   OF   SENSATION  91 

anterior  root  and  certain  muscles  may  be  made  to  contract. 
The  brain  must  be  stimulated  before  there  can  be  percep- 
tion of  a  nervous  impulse.  Through  the  nerve  fibers 
which  run  from  cells  of  the  gray  column  into  and  up  the 
white  columns  of  the  spinal  cord,  the  nervous  impression 
must  be  carried  on  till  it  affects  the  special  nerve  cells  in 
the  particular  portion  of  the  brain  set  apart  for  receiving 
the  particular  kind  of  nervous  stimulus  from  the  particu- 
lar part  of  the  body.  Then  sensation  results,  and  through 
the  influence  of  the  will,  carried  along  the  efferent  motor 
fibers,  motion  may  be  produced  in  the  voluntary  muscles, 
and  a  great  variety  of  acts  may  take  place  in  consequence 
of  the  stimulation  of  the  sensory  organs  in  the  skin. 

Demonstrations  and  Experiments 

28.  Simple  Epithelium.  —  In  connection  with  the  subject  of  the 
skin,  the  general  structure  of  epithelium  may  be  profitably  illus- 
trated. Where  frogs  are  kept  in  captivity,  excellent  examples  of 
simple  epithelium  can  be  obtained  from  the  moulted  skins,  for 
examination  with  the  microscope. 

29.  Ciliated  Epithelium. —li  the  roof  of  a  living  frog's  mouth  be 
scraped  with  a  scalpel  and  the  debris  thus  obtained  be  mounted  in 
normal  salt  solution  on  a  slide,  there  can  be  found,  on  examination 
with  the  microscope,  many  cells  which  show  cilia  moving  actively. 

30.  Squamous  Epithelium.  —  Scrape  the  inside  of  the  cheek  with  a 
scalpel,  mount  the  debris  in  water  on  a  slide,  and  examine  with  the 
microscope.  Irregular  flattened  plates  can  be  distinguished,  singly 
or  in  groups.  In  most  of  them  the  position  of  the  nucleus  can  be 
discerned. 

31 .  Epithelium  in  Section.  —  If  possible,  some  prepared  microscopi- 
cal sections  of  various  kinds  of  epithelium  should  be  studied  by 
the  class.  Sections  of  the  wall  of  the  digestive  tract,  of  the  trachea, 
of  blood  vessels,  etc.,  furnish  excellent  examples. 

32.  Section  of  the  Skin.  —  Specially  prepared  sections  of  human  skin 
can  be  purchased.  Usually  such  sections  contain  hair  follicles,  sweat 
glands,  and  oil  glands. 


92  CONSCIOUS   NERVOUS   OPERATIONS 

33.  The  Epidermis.  —  Observe  that  with  a  needle  a  portion  of  the 
outer  skin  may  be  removed  without  pain  or  flow  of  blood.  If  the 
hands  be  washed  in  warm  water  and  then  dried,  on  rubbing  them 
together  briskly,  portions  of  the  dead  scaly  epidermis  will  be  removed. 

On  the  palm  of  the  hand  the  epidermis  is  seen  to  be  thrown  up  in  a 
series  of  curved  parallel  ridges.  The  latter  are  caused  by  the  projec- 
tions of  the  papillae  of  the  underlying  dermis.  On  examination  with 
a  lens,  large  numbers  of  the  minute  openings  of  the  sweat  glands  may 
be  seen  on  the  ridges  of  the  epidermis. 

34.  Discrimination  in  Touch.  —  Find  the  least  distance  at  which  the 
points  of  a  pair  of  blunt-pointed  compasses  can  be  distinguished  as 
two  points  when  applied  to  the  skin  of  the  arm.  Repeat  the  same 
experiment  on  the  back  of  the  hand,  the  forehead,  the  finger  tips,  and 
the  tip  of  the  tongue.  In  this  way  a  region  of  greatest  sensitiveness 
can  be  distinguished. 

35.  Location  of  Touch.  —  Ask  a  person  to  close  his  eyes,  touch  some 
part  of  his  body  with  a  pencil,  and  ask  him  to  indicate  the  same  point 
with  another  pencil,  immediately  afterward.  He  will  probably  make 
some  errors.  The  experiment  may  be  made  more  interesting  by  repeat- 
ing the  trials,  taking  the  measure  of  each  error  and  averaging  the 
errors.  By  repeating  this  experiment  on  a  number  of  persons,  some 
very  interesting  results  may  be  obtained  and  tabulated. 

36.  Aristotle's  Experiment.  —  Cross  the  middle  over  the  index  finger 
so  that  the  tip  of  the  middle  finger  is  on  the  thumb  side  of  the  index 
finger.  Place  between  the  two  a  marble  or  other  small  object.  A 
sensation  of  two  objects  will  result,  especially  if  the  fingers  be  moved. 

37.  Delicacy  of  Touch.  —  With  small  weights  of  pith  or  cork,  find 
the  least  pressure  that  is  perceptible  on  the  skin  of  the  arm  and  tips 
of  fingers.  The  weights  may  be  applied  by  lowering  them  upon  the 
skin  by  means  of  delicate  silk  fibers  attached  to  them.  The  surface 
which  is  applied  to  the  skin  should  have  the  same  area  in  all  the 
weights,  and  care  should  be  taken  that  the  weights  do  not  move  after 
touching  the  skin.  The  person  experimented  upon  should  keep  the 
eyes  closed  while  the  weights  are  being  applied.  The  weights  should 
also  be  applied  to  the  forehead,  temples,  lips,  and  tongue.  The  main 
purpose  of  this  experiment  is  to  determine  the  regions  of  the  skiu 
most  sensitive  to  contact. 

38.  Hairs  as  Organs  of  Touch.  ^-Ji  the  weights  used  in  the  preced- 
ing experiment  be  applied  to  regions  of  the  skin  possessing  hairs,  it 


THE   SKIN  AS   AN  ORGAN   OF   SENSATION  93 

will  be  found  that  a  weight  touching  a  hair  may  be  felt,  even  though 
its  contact  is  not  perceived  when  it  is  applied  directly  to  the  skin. 

39.  Estimation  of  Weight  hy  Sense  of  Pressure.  —  liest  the  back  of  the 
hand  upon  some  easy  support,  and  place  on  the  palm  a  small  wooden 
or  pasteboard  disk.  Upon  the  latter  place  different  weights.  Find 
the  least  difference  in  weight  that  can  be  detected.  A  great  variety 
of  weights  can  be  obtained  by  loading  empty  cartridges  with  shot  to 
any  desired  extent.  If  the  cartridges  are  all  of  the  same  size,  than  the 
person  experimented  upon  can  not  estimate  the  weight  by  sight.  Sev- 
eral pupils  should  be  experimented  upon,  to  show  variation  in  aeute- 
ness  of  pressure  sense. 

40.  The  Muscular  Sense.  —  Modify  the  preceding  experiment  by 
having  the  weights  lifted  instead  of  simply  allowing  them  to  press  on 
the  hand.  It  will  be  found  that  smaller  differences  can  be  detected 
than  by  pressure  alone.  Demonstrate  that  a  weight  lifted  slowly 
seems  heavier  than  one  lifted  rapidly. 

41.  Sensatio7is  of  Heat  and  Cold.  —  That  there  are  in  the  skin  two 
distinct  varieties  of  nerve  endings  of  the  temperature  sense  can  be 
very  easily  demonstrated  by  carefully  stimulating  any  certain  area  of 
the  skin  with  hot  and  cold  bodies.  Let  a  square  be  marked  off  with 
ink,  on  the  forearm,  and  a  pointed  brass  rod  be  heated  and  then  care- 
fully drawn  across  this  square  in  parallel  lines  in  various  directions. 
Here  and  there  a  sensation  of  heat  will  appear  distinct  from  the  sensa- 
tion of  contact.  The  hot  spots  should  be  marked  with  ink  dots,  as 
they  are  recognized.  Then  in  a  similar  way  go  over  the  square  with 
a  cold  brass  rod.  Cold  spots  will  occasionally  ajDpear,  in  almost  every 
case  distinct  from  the  liot  spots.  The  cold  spots  should  be  marked  in 
ink  of  a  different  color  from  that  of  the  hot  spots. 


CHAPTER   VII 


TASTE   AND   SMELL 


120.  The  mucous  membrane  of  the  mouth  contains  the 
nerve  endings  which  are  affected  by  taste  stimuli.  The  spe- 
cial taste  organs  are 
found  chiefly  in  the 
papillce  of  the  tongue 
and  the  palate. 

121.  The  Tongue  is 
a     mass     of     striped 
muscular  tissue,  with 
fibers  running  in  va- 
rious directions, 
the  whole  organ 
being       covered 
with    mucous    mem- 
brane (Fig.  53).   The 
papillce  of  the  tongue 
are  much  larger  than 
those  of    the   cuticle 
and  are  plainlj^  visi- 
ble to  the  naked  eye. 
In  some   animals,   as 
the  dog  and  cat,  they 
Fig.  53. -The  tongue.  ^^^  prominent 

K  filiform  papillfe.  /  fungiform  i^apilla.  i  i  i 

L  circumvaiiate  papilla.  and  have  horny  spmes 

94 


TASTE   AND   SMELL 


95 


Wall 


Taste  Buds"^: 


Fig.  54. 


Nerves 


Section  of  circumvallate 
papilla. 


which  give  a  marked  roughness  to  the  surface.  On  the 
front  and  sides  of  tlie  tongue  the  papillae  are  generally 
long  and  slender,  and  are 
therefore  called  filiform 
papillce.  Others  with 
broad,  spreading,  mush- 
room-shaped tops  are  scat- 
tered among  the  filiform 
papillpe  and  are  called  fun- 
giform  papillce.  A  third 
variety,  the  largest  of  all,  is 
the  circumvallate  papillce  (Fig.  54).  These  last  are  only 
eight  or  ten  in  number,  and  are  seen  at  the  back  of  a  man's 
tongue,  in  two  rows  converging  to  a  point  backward. 

122.  Taste  Buds.  — In  the  walls  of  the  circumvallate  and 
in  some,  at  least,  of  the  fungiform  papillae  the  end  organs 
for  taste   have  been    found.     These 
consist  of  a  number  of  overlapping 
epithelial  cells,  like  the  leaves  of  a 
bud  (Fig.  ^5>').     The  innermost  core 
of  the  bud  is  a  number   of  slender, 
closely  packed  cells    terminating  in 
fine,  stiff  spikes  which  project  at  the 
surface  of  the  bud.     These  are  the 
taste  cells  and  are  the  essential  part 
of   the    taste    buds.      Around    these 
cells  the   nerve   filaments  from  cer- 
tain  branches    of   the  ninth  pair  of 
cranial     nerves    (the     glossopharyn- 
geal) end  in  brushlike  expansions. 
Branches  from  the  fifth  cranial  nerve  (the  trigeminal) 
are  also  distributed  to  the  tongue,  and  are  believed  by 
many  physiologists  to  be  concerned  in  taste. 


Taste  Cells 


Fig.  55. 

A  isolated  taste  bud,  from 
whose  upper  free  end 
project  the  ends  of  the 
taste  cells. 

B  supporting  or  protect- 
ing cell. 

C  taste  cell. 


96  CONSCIOUS   NERVOUS   OPERATIONS 

Taste  buds  are  affected  so  as  to  distinguish  different 
tastes  only  when  the  substances  submitted  to  them  are  in 
solution.  The  effect  is  increased  by  friction  between  the 
mouth  and  the  tongue. 

123.  Classification  of  Tastes.  — Tastes  are  of  four  sorts  : 
(1)  sweets,  which  are  best  appreciated  by  the  tip  of  the 
tongue  ;  (2)  sour,  or  acid  tastes,  perceived  best  by  the  side 
of  the  tongue  :  (3)  bitter  tastes,  most  affecting  the  back 
of  the  tongue  ;   (4)  salts. 

It  is  believed  that  separate  taste  buds  are  provided,  one 
sort  being  stimulated  only  by  bitter  substances,  one  by 
sweet,  one  by  sour,  and  one  by  salt.  Some  substances 
taste  sweet  at  the  tip  of  the  tongue  and  bitter  at  the  back 
of  it,  because  they  are  able  to  stimulate  two  sorts  of  taste 
buds,  but  one  kind  of  buds  recognizes  only  a  sweet  taste, 
the  other  only  a  bitter  taste. 

124.  Flavors.  —  We  are  accustomed  to  say  and  to  think 
that  we  taste  a  great  variety  of  flavors  in  our  f  oo'd ;  but 
physiologists  tell  us  that  we  really  taste  only  the  four 
flavors  mentioned  above,  while  others  are  recognized  by 
the  sense  of  smell.  This  may  be  tested  by  holding  the 
nostrils  closed  by  the  fingers  while  different  kinds  of  food 
are  eaten.  An  onion  will  not  taste  different  from  a  potato, 
though  one  would  be  known  from  the  other  by  its  texture. 

125.  The  Sense  of  Smell.  —  The  organ  for  receiving  im- 
pressions from  the  minute  particles  called  odors  is  the  mu- 
cous membrane  lining  the  upper  part  of  the  nasal  cavity. 

126.  The  Olfactory  Nerves  are  the  first  pair  of  cranial 
nerves.  They  spring  from  the  olfactory  lobes^  which  are 
prolongations  of  the  hemispheres  of  the  brain  (Fig.  19, 
p.  29)  and  extend  forward  from  the  base  of  the  cere- 
brum. Branches  of  the  nerves  of  smell  are  distributed 
from  the  olfactory  bulbs,  in  which  the  olfactory  lobes  end, 


TASTE    AND   SMELL 


97 


to  the  raucous  membrane  of  the  nasal  j^assages  (Fig.  56), 
where  the  fine    filaments    of   the    nerve   end   in  delicate 

rod  -  shaped  cells 
crowded  in  among 
the  columnar  cells 
of  the  epithelium 
lining  the  nasal 
passages  (Fig.  57). 


Bl»f 


ms 


Fig.  56. —  Section  of  nose,  showing  outer  wall 
of  right  nasal  cavity. 

a,  b,  c,  d  interior  of  uose. 

K  olfactory  bulb,  below  which  are  seen  the  nerve 
fibers  spreading  out  in  the  mucous  membrane. 


Fig.  57.— Cells  from  ol- 
factory membrane. 

E  epithelial  cell. 
N  nerve  cell. 


127.  An  Olfactory  Impression.  —  Odors  are  usually  car- 
ried to  the  membrane  of  the  nose  by  means  of  the  atmos- 
phere, but  they  must  be  dissolved  or  suspended  in  liquid 
before  they  can  affect  the  end  organs  for  smell.  Hence 
the  glands  of  the  olfactory  membrane  lining  the  nasal 
passages,  whose  secretions  keep  the  surface  always  moist, 
are  important  subsidiary  organs.  As  the  air  is  brought 
to  the  membrane  in  ordinary  breathing,  one  is  able  to 
perceive  various  odors  when  moderately  strong.  By 
what  is  called  "  sniffing  "  the  air  is  drawn  into  the  upper 
as  well  as  the  lower  nasal  chambers,  and  more  of  the 
macy's  phys.  —  7 


98  CONSCIOUS  NERVOUS    OPERATIONS 

odoriferous  particles  reach  the  olfactory  cells.  Thus 
one  is  able  to  examine  more  fully  the  odors  of  the  air, 
and  several  different  "  smells  "  may  be  sometimes  distin- 
guishable at  once.  Usually  the  odors  reach  both  nostrils 
at  the  same  time  and  two  impulses  a.re  conducted  along 
the  two  olfactory  nerves  ;  they  are,  however,  fused  into 
one  sensation.  If  different  odors  are  brought  at  one 
time  to  the  olfactory  cells  of  the  two  nasal  passages,  one 
sensation  sometimes  destroys  the  other  ;  sometimes  first 
one  and  then  the  other  odor  is  perceived ;  in  any  case 
there  is  but  one  sensation. 

128.  Other  afferent  impulses  than  those  of  smell  may 
arise  in  the  nasal  membrane.  A  very  pungent  substance, 
such  as  ammonia,  causes  sensation  distinct  from  smell, 
sensation  which  is  found  to  belong  both  to  parts  of  the 
nasal  membrane  on  which  the  olfactory  nerves  ramify 
and  also  to  other  portions. 

A  very  small  quantity  of  odoriferous  material  ig  suffi- 
cient to  excite  the  sensation  of  smell.  A  very  minute 
particle  of  musk,  for  instance,  will  fill  a  large  room  with 
its  odor,  and  that  for  an  indefinitely  long  time. 

The  end  organs  of  the  olfactory  nerves  are  soon  ex- 
hausted, and  sensation  dies  out.  We  soon  cease  to  notice 
the  odors  in  a  room,  though  we  may  have  thought  them 
overpowering  on  entering.  Many  animals  are  much  more 
liberally  endowed  with  the  power  of  detecting  and  discrim- 
inating odors  than  is  man. 

129.  Path  of  an  Olfactory  Impulse.  —  The  olfactory  cells 
in  the  epithelium  of  the  nasal  passages  send  a  process 
to  the  surface  of  the  mucous  membrane,  and  another 
inward  (Fig.  57).  The  latter  process  of  each  cell  ends 
in  fine  spreading  fibrils  which  mingle  with  similar  brush- 
like fibrils  from  a  deeper  layer  of  nerve  cells  in  the  olfac- 


TASTE   AND   SMELL 


99 


tory  lobe.  These  deeper  cells  send  axis  cylinder  processes 
up  and  along  the  olfactory  tract  to  different  centers  in 
the  gray  matter  of  the  cerebrum. 
These  centers  lie  in  the  temporal 
lobe,  back  of  the  eye  (Fig.  58). 

The  olfactory  nerves  have  a 
path  exceptionally  direct  from 
their  external  or  peripheral  end 
to  the  brain  center  in  which 
they  rise.  Just  what  is  the 
connection  between  this  fact 
and  the  other  often  observed 
fact  that  stronger  mental  asso- 
ciations cling  about  sensations 
of  smell  than  about  almost  any 
other  external  impressions,  it  is 
not  easy  to  say. 

Strong  reflex  nervous  action 
often  results  from  excessive  stimulation  of  the  olfactory 
nerves,  as  when  a  person  faints  in  consequence  of  inhal- 
ing certain  odors. 

130.  Effects  of  Alcohol  upon  Taste  and  Smell.  —  The  ha- 
bitual use  of  drinks  containing  alcohol,  of  tobacco,  and  of 
very  strongly  flavored  foods  is  found  to  dull  the  sense  of 
taste,  and  by  alcohol,  at  least,  the  olfactories  are  rendered 
less  acute. 


Fig.  58.  —  Diagram  of  the  path 
of  an  olfactory  impulse. 

The  impulse  passes  from  the 
olfactory  cells  of  the  nose  to  the 
olfactory  bulb  (01. B) ,  and  thence 
to  the  olfactory  center  (01.  C)  on 
the  inner  side  of  the  temporal 
lobe  of  the  cerebrum. 


Demonstrations   and   Experiments 


42.  The  Tongue.  —  By  the  aid  of  a  hand  mirror  the  pupil  can 
easily  distinguish  the  fiUform  and  fungiform  papillae,  on  his  own 
tongue.  The  circumvallate  papillae  lie  so  far  back  that  it  will  be 
found  more  convenient  to  demonstrate  them  on  the  tongue  of  one  of 
the  domestic  animals  (dead). 


100  CONSCIOUS   NEKVOUS    OPERATIONS 

43.  Varieties  of  Tastes.  —  Wipe  the  tongue  dry  and  place  on  its 
tip  a  crystal  of  sugar.  It  is  not  tasted  until  it  dissolves.  Place  a 
crystal  of  sugar  on  the  tip  and  another  on  the  back  of  the  tongue. 
The  sweet  taste  is  more  evident  at  the  tip.  Repeat  the  process,  using 
a  strong  solution  of  quinine  sulphate  dissolved  in  water  by  aid  of 
a  little  sulphuric  acid.  The  bitter  taste  is  most  pronounced  on  the 
back  of  the  tongue.  In  a  similar  way  determine  where  acids  and 
salts  are  tasted,  using  a  1  per  cent  solution  of  acetic  acid  and  a  10  per 
cent  solution  of  common  salt  respectively. 

44.  Organs  of  Smell.  —  The  turbinated  processes  of  the  human 
ethmoid  and  maxillary  bones,  or  those  of  some  of  the  domestic 
animals,  should  be  accessible  to  the  pupil  for  examination,  as  they 
show  how  a  great  deal  of  surface  in  a  small  space  is  provided  for  the 
olfactory  membrane.  The  teacher  should  perform  such  dissections 
upon  the  head  of  some  one  of  the  domestic  animals  as  to  show  the 
olfactory  epithelium,  the  exterior  nasal  passages,  and  the  posterior 
passages  opening  into  the  pharynx. 

45.  Comhination  of  Taste  with  Smell.  —  Close  the  nostrils,  shut  the 
eyes,  and  try  to  distinguish  by  taste  alone  between  an  apple,  a  potato, 
and  an  onion.  Chew  a  grain  of  roasted  coffee  and  notice  how  nearly 
tasteless  it  becomes  when  the  nostrils  are  closed. 

46.  Fatigue  of  Smell.  —  For  several  minutes  smell  continuously  of 
a  piece  of  camphor  gum,  breathing  in  through  the  nose  and  out  through 
the  mouth.  The  intensity  of  the  smell  becomes  much  lessened.  But 
if  some  other  odoriferous  substance,  as  clove  oil,  is  brought  near  the 
nostrils,  it  will  be  found  that  the  fatigue  is  only  for  the  odor  of 
camphor. 


CHAPTER   VIII 

THE  EYE   AND   THE   SENSE   OF   SIGHT 

131.  By  means  of  touch,  taste,  and  smell  the  brain  per- 
ceives external  objects  through  actual  contact  between 
particles  of  matter  from  the  objects  j)erceived  and  the 
human  organism.  But  we  need  to  be  able  to  acquire 
knowledge  of  the  properties  of  objects  at  a  distance  from 
ourselves.  The  sense  of  smell  does  indeed  bring  to  us 
limited  information  respecting  some  classes  of  objects  at 
no  great  distance;  but  it  is  by  means  of  the  eye  and  the 
ear  that  we  gain  our  most  valuable  knowledge  of  the  uni- 
verse, and  througli  these  that  we  enjoy  the  most  refined 
and  elevated  of  all  our  pleasures. 

132.  Vision.  —  When  rays  of  light  fall  upon  a  nervous 
apparatus  so  made  as  to  be  affected  by  that  stimulus,  and 
the  impulse  is  carried  by  a  nerve  to  the  nerve  center  for 
vision,  there  results  the  sensation  of  sight.  Some  animals 
possess  a  simple  arrangement  for  vision,  consisting  of  only 
three  parts.  Certain  modified  parts  of  the  epidermis  are 
stimulated  by  the  light,  nerve  fibers  carry  the  impulse  to 
the  nerve  center,  and  light  is  perceived.  Man,  however, 
is  provided  with  organs  of  vision  of  elaborate  and  com- 
plex structure. 

133.  Lig^ht.  —  All  space  is  believed  to  be  filled  with  an 
extremely  thin,  perfectly  elastic  medium  called  ethei\  in 
which  atoms,  molecules,  and  masses  of  matter  are  immersed 

101 


102  CONSCIOUS  NERVOUS   OPERATIONS 

as  fishes  are  immersed  in  the  sea.  Of  this  ether  little  is 
known,  but  it  is  supposed  to  transmit  energy  by  waves. 
The  energy  resident  in  vibrations  of  the  ether  is  called 
radiant  energy^  and  it  receives  special  names  according  to 
its  special  manifestations.  For  example,  when  it  raises  the 
temperature  of  objects  which  receive  it,  it  is  called  radiant 
heat ;  when  it  causes  chemical  changes,  it  is  called  actinic 
energy;  in  another  form  it  is  known  as  electricity;  Avhen  it 
affects  the  eye  we  call  it  light.  All  these  forms  of  energy 
extend  in  straight  lines  from  the  points  of  origin.  Every 
visible  object  sets  up  waves  in  the  ether  going  in  every 
possible  direction.  Many  millions  of  these  waves  are  pro- 
duced in  a  single  second. 

134.  Color.  —  Some  light  waves  give  to  the  eye  the  sensa- 
tion of  red  color;  these  are  the  longest  of  the  light  waves 
perceived  by  the  eye.  Others  give  us  the  perception 
of  violet  color;  they  are  the  shortest.  Between  them  in 
length  are  the  waves  of  all  the  other  colors.  A  union  of 
these  many  colors  produces  white  light. 

135.  The  Spectrum.  —  When  a  slender  beam  of  sunlight 
is  allowed  to  pass  through  a  small  hole,  and  then  through 

a  glass  prism  into  a 
darkened  room,  the  rays 
of  light  falling  upon  a 
screen  are  seen  in  an 
oblong  band  of  light  of 
many  colors  arranged  as 
we  see  them  in  the  rain- 
bow. This  band  of  col- 
Fig.  59.  — Separation  of  the  rays  of  a 

beam  of  light  by  a  prism.  Ors  IS  called  a   spectrum 

(Fig.  59). 

136.  Refraction.  —  The  separation  of  colors  by  the  prism 
is  due  to  two  facts.     First,  whenever  a  ray  of  light  passes 


THE   EYE   AND   THE    SENSE    OF    SIGHT 


103 


obliquely  from  one  medium  into  anotlier  of  different  den- 
sity, its  direction  is  changed,  the  ray  is  bent,  or  refracted, 
we  may  say.  In  passing  from  the  atmosphere  through  the 
prism,  the  ray  of  light  is  twice  turned  from  its  original 
direction.  Second,  different  colors  are  refracted  in  differ- 
ent degrees;  red  raj's,  or  those  having  the  longest  waves, 
are  bent  least;  the  violet  rays,  those  having  the  shortest 
waves,  most  of  all;  and  the  colors  between  vary  in  this 
respect  in  the  order  of  their  arrangement  in  the  rainbow. 

137.  Images  formed  by  Lenses. — A  lens  is  a  transparent 
medium,  having  at  least  one  curved  surface.  Rays  of  light 
from  any  point  pass- 
ing through  a  lens 
are  bent  either  toward 
each  other  or  more 
widely  apart,  accord- 
ing to  the  arrange- 
ment of  the  surfaces 
of  the  lens.  When  Fig.  60 
they  are  bent  toward 
each  other  they  may 
be  brought  together 
at  a  point  called  the  focus.  If  the  focus  is  allowed  to  fall 
upon  a  screen  or  other  suitable  surface,  an  accurate  image 
of  the  object  from  which  the  rays  come  is  produced 
(Fig.  60).  By  using  a  properly  prepared  plate  the  pho- 
tographer fixes  this  image  and  produces  a  permanent 
picture. 

138.  The  Nervous  Apparatus  for  Vision  may  be  briefly  said 
to  consist  of  :  (1)  the  membrane  of  the  eye,  called  the 
retina^  AA'hich  receives  the  end  filaments  of  the  optic  nerve  ; 
(2)  the  optic  nerve;  and  (3)  the  visual  center-  in  the  brain, 
which  receives  the  stimulus  conveyed  by  the  optic  nerve 


Diagram  of  the  formation  of  an 
image  with  a  lens. 

a  an  object  sending  off  light. 

b  lens.        c  image  of  the  object  a. 


104 


CONSCIOUS   NERVOUS   OPERATIONS 


and  gives  rise  to  the  consciousness  of  sight  (Fig.  61). 
Nerve  fibers  are  also  distributed  to  the  numerous  muscles 

of  the  various  parts  of  the 

eye  and  its  accessories. 

139.  Nerves  of  the  Eye. — 
The  second  pair  of  cranial 
nerves  are  the  optic  nerves 
(Fig.  19,  p.  29).  The  third 
pair  go  to  four  of  the  mus- 
cles which  move  the  eyeball, 
and  are  called  the  oculomotor 
nerves.  The  fourth  and  sixth 
pairs  also  supply  muscles  of 
the  eyeball.  From  the  fifth 
pair  of  nerves  (the  trigemi- 
nal') are  sent  branches  to  the 
lachrymal  glands  and  the 
eyelids. 

140.  Course  of  the  Visual 
Impulse  (Fig.  61). — Rays  of 

light  falling  upon  the  retina  produce  certain  changes 
(chemical  or  other)  in  or  about  the  peculiarly  shaped 
nerve  cells  called  rods  and  cones.  These  changes  excite  a 
nervous  impulse  which  is  conducted  by  the  minute  nerve 
fibers  from  the  rods  and  cones  (the  end  organs  of  vision) 
along  the  optic  nerves  which,  after  passing  through  the 
opening  in  the  back  of  each  eye  socket,  unite  at  Avhat  is 
called  the  opiic  commissure.  Here  many  of  the  nerve 
fibers  cross,  but  some  from  each  eye  pass  on  to  the  nervous 
center  of  the  same  side  ;  so  that  if  the  centers  of  vision  on 
one  side  were  destroyed,  there  would  still  be  sight  in  both 
eyes.  This  crossing  of  the  optic  nerve  fibers  is  called  the 
optic  chiasma  (Fig.  62). 


Fig.  61.  —Diagram  of  path 
of  optic  impulse. 

Three  courses  are  possible  :  (1)  di- 
rectly from  cells  of  retina  to  the 
visual  center  {OG) ;  (2)  through  a 
relay  in  the  oj^tic  thalamus  {T); 
(3)  through  a  relay  in  the  anterior 
corpora  quadrigemina  (Q). 


THE   EYE    AND    THE    SENSE    OF    SIGHT 


105 


Beyond  the  junction  of  the  optic  nerves  the  course  of  a 
visual  impulse  is  called  the  02)tic  tract.     Some  of  the  fibers 
run  directly  to  the  visual  center      q^ 
from  the   retina,   others   pass  to  \~^^.^ 

the    corpora    quadrigemina    and  \     ^^^-.^ 

other  centers  before  reaching  the 
cortex.  The  gray  matter  of  the 
brain  is  regarded  as  the  seat  of 
sense  perception,  and  the  sense 
of  sight  is  believed  to  be  located  ^^^^^.        ^^^^^^ 


-Diagram  of  optic 
chiasma. 

Rays  from  0,  falling  on  the 
similar  regions  of  the  retina 
(D,  D'),  give  rise  to  impulses 
passing  to  the  same  half  of 
the  brain. 


in  certain  groups  of  cells  in  the 
hinder  part  of  the  cerebrum. 

141.  The  Eye.  —  Something 
more  than  the  nervous  apparatus 
above  described  is  needed  to 
enable  one  to  perceive  a  definite 
image  of  a  distant  object.  Light  falling  upon  the  general 
surface  of  a  retina  with  its  conducting  nerves  and  nerve 
centers  would  result  only  in  perception  of  light  and  of 
color.  But  in  the  eye,  lying  in  front  of  the  retina,  are  cer- 
tain refracting  media  which  act  as  lenses  to  converge  the 
rays  of  light  so  that  only  points  of  the  retina  are  affected 
by  them  ;  that  is,  the  rays  are  brought  to  a  focus,  and 
an  image  of  the  object  from  which  the  rays  come  is  pro- 
duced as  in  a  photographer's  camera.  The  eye  lies  in  a 
pyramidal  cavity,  called  the  orhit,  haA^ng  its  apex  directed 
inward  and  backward. 

142.  The  Coats  of  the  Eye.  —  The  eye  is  a  nearly  spherical 
sac  about  one  inch  in  diameter,  made  up  of  .a  firm  wall  of 
tissues  called  the  coats  of  the  eye  (Fig.  63).  The  outer  of 
these,  composed  of  connective  tissues,  is  opaque  except  at 
the  center  of  the  front  of  the  eye,  where  it  becomes  trans- 
parent and  is  called  the  cornea;    the    remainder   of  this 


106  CONSCIOUS   NERVOUS   OPERATIONS 

outer  coat  is  called  the  sclerotic  coat^  and  forms  the  "  white 
of  the  eye."  At  the  back  of  the  eyeball  the  optic  nerve 
pierces  through  this  coat  to  reach  the  retina.  Both  the 
cornea  and  the  sclerotic  coat  on  the  front  of  the  ball  are 
covered  Avith  a  thin  layer  of  modified  mucous  membrane, 
called  tlie  conjunctiva.,  which  is  folded  back  to  form  the 
lining  of  the  eyelids. 


Fig.  63.  —Cross  section  of  the  eye. 

Sc   sclerotic  coat.  Ch  choroid.  0  optic  nerve. 

C     cornea.  /     iris.  B  blind  sj^ot. 

con  conjunctiva.  R    retina.  Y  yellow  spot. 

L  lens.     A  anterior  chamber,  filled  with  aqueous  humor. 

V  posterior  chamber,  filled  with  vitreous  humor. 

A  second  coat  of  the  eyeball  consists  of  the  choroid^ 
made  up  largely  of  blood  vessels  and  loose  connective  tis- 
sue, and  containing  in  the  inner  layers  a  dark  pigment. 
Just  before  it  passes  into  the  iris  —  which  is  that  part 
of  the  choroid  forming  the  colored  ring  in  the  front  of 
the  eyeball,  pierced  by  the  pupil  —  the  choroid  is  laid 


THE   EYE    AND    THE    SENSE   OF   SIGHT 


107 


contracting  narrow 


in  radiating  folds  called  the  ciliary  processes^  which  are 
also  covered  by  the  pigment. 

143.  The  iris  is  a  ring  of  plain,  or  involuntary,  mus- 
cular tissue.  Its  circular  fibers  by 
the  pupil,  while  its  radi- 
ating muscular  or  elastic 
fibers  by  their  contrac- 
tion dilate  the  pupil 
when  the  circular  muscle 
is  relaxed.  Fibers  from 
the  third  cranial  nerve 
are  distributed  to  the 
circular  muscle,  and  oth- 
ers from  the  sympa- 
thetic nervous  system 
are  also  found  in  this 
muscle  of  the  iris.  The 
pigment  of  the  iris  gives 
what  we  call  the  "  color 
of  the  eye."  The  pupil 
is  simply  an  opening 
through  the  iris  into  the 
dark  chamber  beyond. 

144.  The  Retina.— The 
third  of  the  coats  of  the 
eye  is  the  retina.  This 
is  composed  essentially 
of  the  end  libers  of  the 
optic  nerve  and  nerve 
cells,  which,  with  a  supporting  skeleton  of  connective  tis- 
sues, form  a  thin  membrane  lying  loosely  upon  the  choroid 
and  covering  it  as  far  as  the  ciliary  processes.  The  retina 
is  too  complex  to  admit  of  full  description  here.     Though 


A  '  B 

Fig.  64. —Section  of  the  retina. 

A  diagram  of  the  structure  of  the  retina 
as  seen  with  the  compound  microscope. 

B  the  essential  nervous  elements  of  the 
retina  as  demonstrated  hy  the  Golgi 
method. 

1  internal  limiting  memhrane. 

2  nerve-fiber  layer. 

3  nerve-cell  or  ganglion-cell  layer. 

4  inner  molecular  layer. 

5  inner  granular  layer. 

6  outer  molecular  layer. 

7  outer  granular  layer. 

8  external  limiting  memhrane. 

9  rod-and-cone  layer. 
10  pigment-cell  layer. 


108 


CONSCIOUS   NERVOUS   OPEEATIONS 


only  about  one  fiftieth  of  an  inch  in  thickness  at  the  point 
opposite  the  pupil,  where  it  is  thickest,  it  consists  of  ten 
different  layers  (Fig.  64).  Beginning  with  the  side  toward 
the  center  of  the  eyeball,  the  first  layer,  called  the  internal 
limiting  membrane^  is  in  contact  with  the  vitreous  humor 
which  fills  the  largest  cavity  of  the  eye  (§  146),  while  the 
tenth,  or  pigment-cell  layer,  is  next  the  choroid. 

In  the  second  layer,  that  of  the  optic  nerve  fibers,  tlie 
minute  filaments  of  the  optic  nerve  are  distributed.  From 
this  second  layer  they  turn  backward  to  enter  the  deeper 
layers  of  the  retina. 

The  third  layer  is  that  of  ganglion  cells.      They  are 

large  nucleated  cells. 

Direction  of  Light  through  Retina  ,  wllOSC    axls  Cylinder 

processes  are  con- 
tinuous with  the 
optic  nerve  iibers 
of  the  second  layer. 
In  the  ninth  layer 
are  found  nerve  cells 
of  peculiar  shapes, 
calledrocZs  andco/ies. 
There  are  more  rods 
than  cones,  three  or 
four  rods  usually 
lying  between  two 
cones.  It  is  under- 
stood that  in  these  cells  arises  the  nervous  impulse  Avhich 
results  in  vision. 

From  the  pigment-cell  layer  extends  a  thick  fringe  to 
support  the  outer  ends  of  the  rods.  Many  of  the  rays  of 
light  which  fall  upon  the  retina  are  absorljed  by  the  pig- 
ment, only  a  small  part  of  the  rays  being  reflected  back 


Optic^Nerve 

Fig.  65.  —Diagram  of  a  section  of  the  retina. 

Showing  that  the  rays  pass  from  the  anterior 
to  the  posterior  parts  of  the  retina  to  reach  the 
rods  and  cones.  From  the  latter  the  optic  im- 
pulse passes  to  the  anterior  parts  of  the  retina, 
and  thence  by  the  optic  nerve  iibers  through  the 
posterior  parts  to  the  brain. 


THE   EYE   AND   THE    SENSE   OF   SIGHT  109 

through  the  pupil.      Heuce  the  iuterior  of  the  eye  usually 
looks  black. 

145.  The  Yellow  Spot  and  the  Blind  Spot  (Fig.  63).  —  The 
retiua  is  uot  equally  sensitive  to  light  over  its  whole 
surface.  Only  upon  a  single  spot,  about  one  twenty- 
fourth  of  an  inch  in  diameter,  are  perfectly  definite  out- 
lines of  images  formed.  This  is  called,  from  its  color, 
the  yellow  spot. 

About  one  tenth  of  an  inch  from  the  inner  side  of  the 
yellow  spot  is  the  optic  disk,  or  blind  spot^  an  elevated 
surface  where  the  optic  nerve  fibers  enter  the  eye.  These 
are  conducting  nerve  fibers  only,  not  stimulated  by  light, 
and  that  spot  is  therefore  blind. 

Delicate  fibers  from  the  optic  nerve  run  straight  to  the 
yellow  spot.  Here  the  layer  of  ganglion  cells  is  much 
thicker  than  elsewhere,  and  in  the  rod-and-cone  layer  of 
the  yellow  spot  no  rods,  but  cones  only,  are  found. 

In  the  very  center  of  the  yellow  spot  is  a  colorless 
depression,  or  pit,  from  which  the  various  layers  of  the 
retina  have  nearly  disappeared,  leaving  only  the  rod  and 
cone  layer.  This  is  the  point  of  most  acute  vision,  the 
spot  upon  Avhich  the  image  falls  when,  wishing  to  see  with 
the  utmost  distinctness,  we  look  ''  straight  at "  an  object. 

146.  The  Lenses  (Fig.  63).  —  The  refracting  media  of  the 
eye  are  four  in  number.  (1)  The  coniea  has  already  been 
defined.  (2)  The  crystalline  lens  is  a  transparent,  double- 
convex  body  about  one  third  of  an  inch  in  diameter  and 
one  fourth  of  an  inch  thick,  lying  just  back  of  the  pupil 
and  kept  in  place  by  a  sheet  of  transparent  membrane 
called  the  suspensory  Uyament  attached  to  the  circum- 
ference of  the  lens  and  to  the  ciliary  p)rocesses.  (3)  The 
space  between  the  iris  and  the  cornea,  called  the  anterior 
chamber.,  is  filled  Avith  a  thin  fluid  like  water,  called  the 


110  CONSCIOUS   NERVOUS   OPERATIONS 

aqueous  humor.  (4)  The  larger  cavity  of  the  eyeball, 
behind  the  iris  and  the  crystalline  lens,  called  the  posterior 
chamber.,  is  filled  with  a  transparent,  semifluid,  jellylike 
substance  called  the  vitreous  humor. 

147.  The  Muscles  of  the  Eyeball  and  their  Nervous  Supply 
(Fig.  66).^ — Each  eye  is  moved  by  six  muscles,  four  of 

which  are  straight  and  two  ob- 
lique. The  straight,  or  rectus, 
muscles  have  one  end  attached 
to  the  margin  of  the  opening  in 
the  orbit  through  which  the 
optic  nerve  and  accompanying 
blood  vessels  pass,  while  the 
Fig.  66. -Muscles    of  the     q^\^q^  ^g  inserted  into   the    eye- 

"^     ^    ■  ball.     The  internal  rectus  muscle, 

inserted  on  the  nasal  side  of  the  eyeball,  turns  the  ball 
inward ;  the  external  rectus^  inserted  on  the  outer  or  tem- 
poral side,  turns  it  outward.  The  superior  rectus^  inserted 
on  the  upper  and  forward  side,  pulls  the  eye  upward ;  the 
inferior  rectus^  inserted  on  the  under  and  forward  part  of 
the  ball,  draws  it  down. 

The  remaining  muscles  are  called  the  superior  and  the 
inferior  oblique,  and  they  unite  with  the  straight  muscles 
to  move  the  eyeballs  inward  and  upward,  inward  and 
downward,  outward  and  upward,  outward  and  dowuAvard, 
and  to  produce  a  measure  of  rotation  upon  an  axis.  The 
superior  oblique  muscle  arises  near  the  straight  muscles  in 
the  edge  of  the  orbit.  Near  its  forward  end  it  narroAvs 
into  a  tendon  which  passes  through  a  ring  of  fibrocartilage 
attached  to  a  notch  in  the  frontal  bone  which  bounds  the 
front  and  upper  margin  of  the  orbit ;  the  end  of  the  tendon 
is  then  inserted  into  the  upper  side  of  the  eyeball.  The 
cartilage  ring  acts  as  a  pulley  to  change  the  direction  of 


THE   EYE   AND   THE    SENSE   OF   SIGHT  111 

the  muscular  action.  The  inferioy^  oblique  muscle  arises 
near  the  front  of  the  orbit  and  at  its  inner  side,  whence  it 
passes  under  the  ball  and  nearly  halfway  round  it,  to  be 
inserted  into  the  back  part  on  the  temporal  or  outer  side. 

148.  The  muscles  of  the  two  eyes  act  simultaneously 
so  that  the  two  retinas  may  receive  images  from  the  same 
objects  at  the  same  time  and  upon  corresponding  portions 
of  their  surfaces.  The  external  rectus  of  the  right  eye 
contracts  at  the  same  time  as  the  internal  rectus  of  the  left 
eye,  turning  both  eyes  to  the  right,  and  vice  versa.  All 
these  muscles  are  supplied  with  nerves  from  the  third  pair 
of  cranial  nerves,  except  the  superior  oblique,  which  is 
sujDplied  by  the  fourth,  and  the  external  rectus,  which  is 
supplied  by  the  sixth. 

149.  The  Ciliary  Muscles  and  Nerves.  —  Besides  the  mus- 
cles Avhich  move  the  eyeball  as  a  whole,  certain  muscles 
within  the  eyeball  have  to  do  with  vision.  These  are  the 
muscles  of  the  iris,  which  vary  the  area  of  the  pupil,  and 
the  ciliary  muscles^  which  accommodate  the  eye  for  differ- 
ent distances  by  altering  the  shape  of  the  lens,  as  will  be 
explained  a  little  later.  The  ciliary  nerves  supply  these 
muscles.  They  are  com^Dosed  of  fibers  from  the  third  and 
fifth  cranial  nerves  with  others  from  the  sympathetic  sys- 
tem. Branches  from  the  ciliary  nerves  are  distributed 
also  to  the  cornea. 

150.  Other  Appendages  of  the  Eye  ( Fig.  67).— Each 
eyeball  lies  in  its  orbit  upon  a  soft  cushion  of  fat,  and  the 
cavity  also  contains  connective  tissue,  blood  vessels,  and 
nerves.  The  front  of  the  eye  is  protected  by  the  eyelids^ 
which  are  two  folds  of  skin  stiffened  by  thin  plates  of 
fibrous  tissue.  Along  the  edges  of  the  lids  arise  rows  of 
curved  hairs,  called  eyelashes^  which  serve  to  protect  the 
eye  from  dust,  and  furnish  a  slight  shade.      On  the  inner 


112 


CONSCIOUS  NERVOUS   OPERATIONS 


edges,  in  little  grooves,  are  minute  glands  from  which  an 
oily   secretion    flows  to  the    free   edges   of   the   lids    and 

prevents  their  adhesion 
when  closed.  Above 
the  orbits  the  thick 
ridges  set  with  hairs, 
called  eyebrows^  also 
serve  to  shield  and 
shade  the  eye. 

In  a  depression  in  the 
upper  and  outer  part  of 
the  orbit  lies  the  lach- 
rymal gland ^  with  ducts 
023ening  on  the  inner 
surface  of  the  upper 
lid.  It  secretes  a  wa- 
tery fluid  designed  to 
lubricate  the  surface  of 
the  eyeball.  When  stimulated  by  the  irritation  of  the 
mucous  membrane  of  the  eye,  the  nose,  or  the  mouth,  or 
by  strong  mental  emotion,  the  lachrymal  fluid  becomes 
excessive,  and  is  called  tears.  Canals  or  ducts  placed  at 
the  inner  angle  of  the  eye  carry  off  the  ordinary  supply 
of  lachrymal  fluid  to  the  nasal  passages.  Branches  from 
the  fifth  (trigeminal)  cranial  nerve  supply  this  gland  and 
send  fibers  also  to  the  eyelids  and  to  inner  portions  of  the 
eyeball. 

151.  The  Eye  as  an  Optical  Instrument. — As  has  been 
said,  the  eye  is  like  a  photographer's  camera  ohscura^  the 
various  parts  of  which  all  have  to  do  with  the  produc- 
tion of  distinct  images  of  external  objects  upon  the  back 
portion  of  the  box;  that  is,  in  the  camera  upon  the  ground 
glass  screen,  in  the  eye  upon  the  nervous  membrane  called 


Fig.  67.— Front  view  of  the  right  eye, 
showing  the  position  of  the  lachrymal 
apparatus. 

G  lachrymal  gland. 

CC  upper  and  lower  lachrymal  ducts. 

B  naso-lachrymal  duct. 


THE    EYE   AND   THE    SENSE   OF    SIGHT 


113 


the  retina  (Fig.  68).     In  the  camera  a  glass  lens  serves 
to  bring  the  rays  of  light  to  a  focus  upon  the  screen.     In 


Fig.  68.  — Formation  of  an  image  on  the  retina. 


the  eye  the  cornea  and  the  crystalline  lens  accomplish  the 
same  object. 

152.  Accommodation  (Fig.  69). — The  camera  is  pro- 
vided with  an  apparatus  for  changing  the  distance  of  the 
lens  from  the  sensitive  plate  or  screen,  so  that  light  from 
objects  at  different  distances  may  be 
focused.  The  eye  is  likewise  supplied  by 
means  of  what  is  called  accommodation^ 
which  is  the  power  of  the  eye  to  adjust 
itself  to  objects  at  different  distances. 
This  power  is  due  primarily  to  the  varia 
ble  shape  of  the  crystalline  lens.  In  the 
camera,  the  lens  and  the  screen  which 
receives  the  image  are  moved  nearer  to- 
gether or  farther  apart  in  order  to  change 
the  focus.  In  the  eye  the  same  object  is 
gained  by  changing  the  convexity  of  the 
lens  itself.  This  is  accomplished  by  the 
contraction  and  relaxation  of  the  ciliary  muscle^  which  lies 
just  beyond  the  outer  margin  of  the  iris  in  the  front  part 
■8 


Fig.  69.  —  Dia- 
gram show- 
ing how  the 
lens  changes 
its  form. 


MJ^CY'8   PHTS. 


114  CONSCIOUS   NERVOUS   OPERATIONS 

of  the  choroid  coat.  It  consists  of  plain  muscle  fibers, 
whose  nervous  supply  comes  from  the  third  cranial  nerve. 
The  ciliary  muscle  is  attached  to  the  ciliary  processes,  and 
these  to  a  membrane  called  the  suspensory  ligament. 
This  ligament  is  secured  also  to  the  circumference  of  the 
lens  in  such  a  way  that  when  the  eye  is  at  rest  it  is  in  a 
state  of  tension,  which  causes  it  to  pull  upon  and  slightly 
flatten  the  lens.  This  keeps  the  eye  at  the  focus  neces- 
sary for  seeing  clearly  objects  at  a  distance  of  perhaps 
twenty  or  twenty -five  feet.  When  the  eye  is  directed  to 
a  nearer  object,  the  fibers  of  the  ciliary  muscle  contract, 
thereby  drawing  forward  the  ciliary  processes,  and  thus 
lessening  the  tension  on  the  suspensory  ligament,  and  the 
elasticity  of  the  lens  causes  it  to  push  forward,  or  become 
more  convex  on  its  front  surface.  This  shortens  the  focal 
distance,  that  is,  causes  the  rays  of  light  to  converge  more 
rapidly.  The  cornea  alone  is  capable  of  forming  distinct 
images,  and  the  chief  function  of  the  crystalline  lens  seems 
to  be  that  of  accommodation. 

153.  Function  of  the  Iris.  — The  iris  (Fig.  63)  is  an  adjust- 
able curtain,  designed,  by  narrowing  the  pupil,  to  cut  off 
a  portion  of  the  light  which  might  render  the  image  con- 
fused, and  to  prevent  too  strong  a  light  from  entering  the 
interior  of  the  eye.  This  change  in  the  size  of  the  pupil 
is  effected  by  the  contraction  and  relaxation  of  its  mus- 
cular tissue,  under  control  of  the  ciliary  nerves. 

154.  Inversion  of  Images  (Figs.  60  and  68). — As  in  a 
camera,  so  in  the  eye  the  image  formed  is  inverted.  The 
rays  of  light  cross  in  being  brought  to  a  focus,  so  that 
the  picture  of  a  man,  a  house,  or  a  tree  on  the  retina  is 
upside  down,  and  also  much  smaller  than  the  object  itself. 
The  reason  why  we  do  not  see  objects  inverted  and  re- 
duced in  size  is  because  it  is  not  the  picture  on  the  retina 


THE    EYE   AND   THE    SENSE   OF   SIGHT  115 

that  we  see,  but  the  object  itself.  Sensation  is  not  in  the 
eye,  but  in  the  brain^  or  in  the  mind  acting  through  the 
brain.  It  is  only  by  study  and  research  that  we  learn 
the  fact  of  the  inverted  image  in  the  eye,  and  meantime 
we  are  accustomed  to  supplement  our  visual  impressions 
by  the  use  of  our  muscles  and  our  organs  of  touch.  The 
hand  interprets  the  impression  on  the  eye,  and  we  learn 
to  see  objects  in  their  true  positions.  We  judge  of  their 
positions  by  the  direction  from  which  the  light  comes  to  the 
eye,  and  of  their  size  by  a  variety  of  experiences  which 
complete  the  impression  given  by  sight.  The  figure  on 
the  retina  has  little  or  nothing  to  do  with  those  judgments. 

155.  Seeing  with  Two  Eyes.  —  Two  images  of  one  object 
are  formed  on  the  two  retinas,  and  two  optic  nerves  and 
tracts  convey  the  impression  to  the  two  opposite  sides  of 
the  brain.  Why,  then,  do  we  not  see  two  objects  ?  Here 
again  we  must  remember  that  our  perceptions  are  never 
simple,  due  to  the  action  of  a  single  organ  and  an  isolated 
set  of  nervous  connections.  Probably  in  every  act  of 
perception  the  nervous  system  acts  as  a  whole  through 
the  intricate  interlacing  of  nervous  fibers  and  the  close 
connections  of  the  cells  in  the  various  nerve  centers.  An 
impression  upon  one  set  of  end  organs  is  supplemented 
and  corrected  by  a  great  number  of  familiar  perceptions 
of  diverse  sorts  brought  before  the  mind  by  memory,  so 
that  the  resulting  judgment  is  an  act  too  intricate  and 
complex  to  be  disentangled.  We  come  to  think  of  the 
object  as  we  know  it  from  all  these  combined  impressions, 
and  not  from  a  single  one  of  them.  Perception  is  the 
result  of  association  and  experience  combined  with  the 
physical  processes  involved. 

156.  Advantages  of  Two  Eyes.  —  For  perfect  vision  the 
retinal  images  must  be  formed  upon  corresponding  portions 


116  CONSCIOUS  NERVOUS   OPERATIONS 

of  the  two  retinas.  The  two  pictures  are  not,  however, 
identical.  The  right  eye  will  see  more  of  one  side  of  an 
object  than  will  the  left,  and  the  left  eye  will  see  more  of 
the  opposite  side.  This  enables  us  to  form  more  accurate 
judgments  of  form  and  distance  than  would  be  possible 
with  only  one  eye.  Then,  too,  one  eye  may  be  wholly 
destroyed  and  a  person  may  still  retain  distinct  vision. 

157.  Duration  of  Sight  Sensation. — The  impression  made 
upon  the  retina  by  a  flash  of  light  remains  for  about  one 
eighth  of  a  second,  so  that  if  flashes  of  light  follow  one 
another  at  a  shorter  interval  than  that  they  appear  as 
one  continuous  impression.  Children  make  a  circle  of 
fire  by  whirling  rapidly  a  lighted  stick,  and  the  spokes  of 
a  swiftly  revolving  wheel  appear  continuous.  If  one  looks 
at  the  sun  or  other  bright  object  and  then  closes  the  eyes, 
he  Avill  continue  for  an  instant  to  see  the  object.  These 
delusive  appearances  are  due  to  the  fact  that  the  nervous 
impressions  made  by  light  upon  the  end  organs  in  the  ret- 
ina remain  after  the  removal  of  the  rays  which  excite  them. 

158.  Fatigue  of  the  Retina.  —  While  the  retina  is  extremely 
sensitive  it  is  also  easily  fatigued.  If  one  looks  steadily 
for  a  time  at  a  bright  object  and  then  turns  the  eye  away, 
he  will  still  see  the  outline  of  the  bright  object,  but  it  will 
be  dark.  This  is  because  that  part  of  the  retina  upon 
which  the  light  fell  from  the  bright  body  has  become  wea- 
ried and  no  longer  resjjonds  to  the  stimulus  of  light.  If 
the  body  looked  at  is  of  a  bright  yellow  color,  the  figure 
seen  when  the  eye  is  turned  away  will  be  blue,  because 
the  retina  is  no  longer  able  to  respond  to  the  stimulus  of 
yellow  rays,  but  is  affected  by  the  rays  of  the  complemen- 
tary color. 

159.  Defects  of  Vision.  —  It  is  very  common  to  see  per- 
sons wearing  lenses,  or  •' glasses,"  to  correct  what  is  called 


THE   EYE    AND   THE    SENSE   OF   SIGHT  117 

"shortsightedness/'  or  ''hmgsightedness."  In  short- 
sighted persons  the  ra^'s  which  in  normal  eyes  come  to  a 
focus  exactly  upon  the  retina  meet  at  a  point  in  front  of 
it,  so  that  no  distinct  image  is  formed.  The  eye  is  too 
long  from  front  to  back,  and  the  difficulty  must  be  cor- 
rected by  using  lenses  which  will  carry  the  focus  back  to 
the  surface  of  the  retina  (Fig.  TO). 


Tig.  70— Diagram  showing  position  of  retina. 

In  natural  sight  (B) .        In  far  sight  (G) .        In  near  sight  (C). 

Those  who  habitually  ase  their  eyes  for  seeing  only 
objects  near  at  hand  are  apt  to  become  shortsighted.  It 
has  been  found  that  children  who  have  grown  up  in 
crowded  parts  of  smoky  London,  wdtli  little  opportunity 
for  looking  off  long  distances,  are  very  often  nearsighted. 
On  the  other  hand,  sailors  and  others  accustomed  to  use 
the  eye  constantly  for  distant  vision  grow  longsighted. 
Their  eyes  become  shortened  from  front  to  back,  so  that 
the  focus  for  ordinary  vision  is  beyond  the  retina. 

As  persons  grow  old  the  eye  usually  becomes  flattened 
on  this  axis,  and  glasses  are  needed  to  converge  the  rays 
of  light  more  rapidly. 

160.  Squinting,  etc.  —  The  muscles  of  the  two  eyes  act 
simultaneously  so  that  the  visual  images  are  formed  upon 
corresponding  parts  of  the  two  retinas.  But  if  the  internal 
rectus  muscle  of  one  eye  is  paralyzed,  or  for  some  reason 


118  CONSCIOUS  NERVOUS   OPERATIONS 

tlie  external  rectus  is  too  short,  that  eye  will  tiu^n  outward 
and  defective  vision  will  result.  If  the  external  rectus  is 
paralyzed,  the  person  will  be  cross-eyed,  or  squint-eyed. 
Paralysis  of  either  of  the  nerves  distributed  to  the  muscles 
of  the  e3^e  will  result  in  abnormal  action  of  those  muscles. 

161.  Astigmatism.  —  Another  defect,  known  as  astigma- 
tism^ is  due  to  the  irregular  curvature  of  the  cornea  or  the 
lens  or  both.  The  eye  may  be  more  convex  on  one  merid- 
ian than  on  others,  so  that  rays  of  light  falling  upon  one 
part  of  the  cornea  (which  is  most  frequentl}'  affected)  are 
brought  to  a  focus  at  a  different  spot  from  the  raj^s  which 
pass  through  other  parts.  Thus  the  image  on  the  retina 
is  indistinct  and  the  vision  is  blurred. 

162.  Color  Blindness.  —  Some  persons  are  unable  to  dis- 
tinguish certain  colors  from  certain  other  colors.  They 
are  said  to  be  color  blind.  Usually  they  differ  from 
persons  of  normal  sight  in  their  inability  to  distinguish 
red  from  green.  Sometimes  only  one  eye  is  color  blind, 
the  other  being  normal.  The  reasons  for  these  phenom- 
ena belong  to  the  abstruse  subject  of  color  sensation, 
which  is  beyond  the  scope  of  this  work. 

The  power  to  distinguish  colors  accuratel}^  is  of  great 
importance  to  those  engaged  in  certain  occupations,  —  for 
example,  to  those  employed  upon  railways,  who  are  re- 
quired to  undergo  examinations  which  test  their  eyes  in 
that  particular. 

163.  Training  of  the  Eye.  —  The  eyes  of  the  young  may 
be  easily  trained  by  practice  under  a  teacher's  guidance 
to  see  quickly  and  accuratel}',  and  to  judge  correctly  as  to 
the  size  of  objects,  distances,  etc.  Such  training  is  of 
great  value  in  all  circumstances  of  life.  It  is  indeed 
more  strictly  a  training  of  the  mind  than  of  the  eye, 
but  may  be  fitly  mentioned  in  tliis  connection. 


THE   EYE    AND   THE    SENSE   OF   SIGHT  119 

164.  Care  of  the  Eye.  —  More  than  some  other  organs, 
the  eye  depends  for  its  healthy  condition  upon  the  gen- 
eral health  of  the  system.  If  that  is  impaired,  the  eye 
is  often  weakened  and  liable  to  disease.  The  children  of 
the  poor,  who  are  ill-nourished  and  inadequately  clothed, 
oftener  suffer  from  sore  eyes  and  defective  vision  than 
do  those  in  better  circumstances.  Living  in  filthy  sur- 
roundings or  rubbing  the  eyes  with  dirty  hands  often 
provokes  diseases  of  the  eyes  and  eyelids.  Some  forms  of 
general  disease  —  measles,  diphtheria,  scarlet  fever,  for  ex- 
ample—  are  apt  to  leave  the  eyes  for  some  time  in  a 
sensitive  condition  and  in  need  of  special  care.  Many 
eyes,  even  those  of  young  children,  are  abnormal  in  re- 
spect to  focalization,  and  the  defect  is  often  unsuspected 
until  a  child  has  endured  much  inconvenience  or  even 
suffering.  Hence  it  is  well  for  the  eyes  of  every  child 
to  be  examined  by  a  competent  oculist,  and  to  have  any 
defects  corrected  by  suitable  glasses.  Children  in  school 
often  suffer  from  severe  headaches  and  appear  dull  at 
their  studies  simply  because  of  easily  remedied  defects  of 
vision. 

165.  Very  strong  light  should  never  be  allowed  to  enter 
the  eye  directly.  When  reading,  sewing,  writing,  etc., 
one  should  sit  so  that  the  light  will  fall  upon  the  work 
from  the  left  side  without  shining  into  the  eyes.  But 
one  should  not  read  or  write  with  direct  sunlight  falling 
upon  the  paper.  Lamps  should  be  provided  with  shades 
to  shield  the  eyes,  and  the  light  should  be  steady,  for  a 
flickering  light  is  exceedingly  trying  to  the  eye. 

Too  faint  a  light  also  strains  the  eye.  One  should  not 
read  or  work  by  twilight,  or  by  any  light  too  dim  to  per- 
mit the  book  or  work  to  be  clearly  seen  at  about  eighteen 
inches  from  the  eyes.      Eyes  may  be  made  nearsighted 


120  CONSCIOUS   NERVOUS   OPERATIONS 

by  carelessly  acquiring  a  habit  of  holding  books,  etc., 
nearer  than  is  necessary. 

Reading  while  in  a  moving  railway  train  or  carriage 
is  bad  for  the  eyes,  as  the  motion  necessitates  constant 
adjustment  of  the  eyes  to  varying  distance,  and  the  power 
of  accommodation  is  overstrained. 

It  is  well  when  using  the  eyes  closely  to  raise  them 
often  and  look  off  to  a  distance,  or  to  close  them  for  a 
moment  of  rest. 

Warm  or  tepid  water  is  better  than  cold  water  for  bath- 
ing the  eyes.  A  compress  wet  in  very  hot  water  and  laid 
over  the  eyes  a  few  minutes  at  a  time,  several  times  a  day, 
will  cure  slight  inflammation,  or  relieve  the  weariness  of 
the  eyes  after  close  application. 

166.  Effects  of  Drinks  containing  Alcohol  upon  the  Eye.  — 
Through  its  influence  upon  the  nerves  and  the  muscles, 
the  continued  and  too  free  use  of  alcohol  renders  the  eye 
unsteady  and  its  adjustment  uncertain  ;  the  small  blood 
vessels  become  dilated,  and  the  eyes  are  blood-shot  and 
often  inflamed.  The  optic  nerve  is  frequently  affected, 
causing  dimness  of  vision,  and  specific  diseases  of  parts 
of  the  eye  may  result,  such  as  cataract  and  disorders  of 
the  retina.  The  confirmed  inebriate  is  the  victim  of  dis- 
eased conditions  in  which  the  sight  becomes  untrust- 
worthy. He  sees  horrible  visions,  frightful,  venomous 
creatures  appear  to  threaten  him,  and  he  is  haunted  by 
specters.  Under  his  imaginary  suffering  he  may  become 
a  raving  maniac,  and  repeated  attacks  of  the  disease  are 
likely  to  prove  fatal. 

Demonstrations  and  Experiments 

47.  Dissection  of  the  £//e.— The  eye  of  the  sheep  or  of  the  ox 
should  be  studied-     It  may  be  examined  fresh  or  after  preservation 


THE   EYE   AND   THE   SENSE    OF   SIGHT  121 

in  one  of  the  fluids  used  in  hardening  and  preserving  the  brain 
(Ex.  6).  First,  the  six  muscles  of  the  eyeball  should  be  noticed  and 
identified.  To  examine  the  internal  structures  an  equatorial  incision 
should  be  made  about  halfway  between  the  cornea  and  the  back  part 
of  the  eyeball,  thus  dividing  the  eye  into  two  parts.  The  structures 
thus  made  visible  can  be  identified  by  reference  to  the  corresponding 
parts  of  the  text.  If  the  teacher  has  any  knowledge  of  histological 
methods,  some  excellent  sections  for  study  with  the  microscope  can 
be  prepared  by  hardening  the  eye  of  a  rat  or  frog  in  Perenyi's  fluid 
for  two  or  three  days,  following  with  alcohols  of  increasing  strength, 
infiltrating  and  embedding  in  celloidin,  and  sectioning  on  a  micro- 
tome. Sections  made  horizontally  through  the  entire  eyeball,  and 
properly  stained,  show  not  only  the  different  coats  and  inclosed 
structures  m  situ,  but  the  different  layers  of  the  retina,  the  entrance 
of  the  optic  nerve,  or  blind  spot,  and  the  yellow  spot.  Similar  sec- 
tions can  be  purchased. 

48.  Refracting  Media.  —  Refraction  of  light  should  be  demonstrated 
by  means  of  lenses  of  various  forms.  Especial  attention  should  be 
given  to  the  formation  of  images  by  convex  lenses.  The  office  of 
the  lens  of  the  eye  can  be  shown  by  removing  it  from  the  eye  of  a 
recently  killed  animal  and  allowing  the  direct  rays  of  the  sun  to  be 
focused  by  it. 

49.  Inversion  of  the  linage  on  the  Retina.  —  This  can  be  very  easily 
shown  by  cutting  away  the  posterior  part  of  the  sclerotic  coat  of  a 
fresh  ox  eye,  leaving  the  retina  intact.  Then  on  turning  the  cornea 
toward  some  bright  object,  as  a  candle  flame,  an  inverted  image 
of  the  object  may  be  seen  shining  through  the  retina.  The  image 
appears  much  clearer  if  the  eye  is  placed,  cornea  forward,  in  a  tube 
of  blackened  paper. 

50.  Model  for  demonstrating  the  Optical  Properties  of  the  Eye.  —  At 
little  labor  and  expense  the  teacher  or  pupil  can  construct  simple  appa- 
ratus that  will  illustrate  many  of  the  optical  features  of  the  eye.  Pre- 
pare an  oblong  box  from  twelve  to  eighteen  inches  long,  open  on  one 
side,  and  blackened  within  (Fig.  71).  One  end  should  be  perforated  in 
the  center  by  an  opening  one  half  to  one  inch  in  diameter,  to  represent 
the  pupil  of  the  eye.  A  watch  crystal  can  be  fastened  over  tlie  open- 
ing, outside,  to  represent  the  cornea.  The  amount  of  light  admitted 
through  the  opening  in  the  box  can  be  regulated  by  means  of  paper 
diaphragms  with  different-sized  perforations.    Inside  the  box  a  reading 


122 


CONSCIOUS   NEEVOUS   OPERATIONS 


glass  or  other  biconvex  lens  can  be  arranged  on  a  support,  so  as  to  focus 
the  rays  of  light  admitted  through  the  pupil  upon  a  movable  screen  at 
the  back  part  of  the  box.  A  serviceable  ground  glass  screen  can  be  made 
by  rubbing  a  piece  of  ordinary  window  glass  with  emery  powder  and 
water.  The  box  is  left  open  on  one  side  to  permit  observation  and 
manipulation ;  but  while  experimenting  the  observer  will  find  it  neces- 
sary to  exclude  all  light,  except  that  which  enters  through  the  end  of 
the  box.  This  can  be  done  by  covering  the  box  and  the  head  of  the  ob- 
server with  a  black  cloth.    While  with  this  apparatus  one  can  illustrate 


W/////////////////////////////. 


Diaphragm.  {Iris) 


yy///////////^^/. 


Fig.  71.  —  Apparatus  for  illustrating  the  optical  properties  of  the  eye. 


most  of  the  characteristic  optical  features  of  the  eye,  yet  obviously  it 
shows  nothing  regarding  the  functions  of  the  aqueous  and  vitreous 
humors.  It  must  be  borne  in  mind,  also,  that  in  the  eye  accommo- 
dation for  objects  of  different  distances  is  brought  about  by  changes 
in  the  form  of  the  lens ;  here  in  the  model  by  changes  in  the  position 
of  the  lens.  Shortsightedness  and  longsightedness  can  be  very  easily 
illustrated ;  also  the  means  of  correcting  them  by  spectacles.  Astig- 
matism can  also  be  shown  by  holding  in  front  of  the  artificial  cornea 
a  bottle  with  sides  of  unequal  curvature,  filled  with  water, 

51.  Accommodation.  —  Hold  up  the  forefinger  six  or  eight  inches 
from  the  eye.  Close  one  eye  and  look  at  the  finger ;  it  appears  dis- 
tinct, while  objects  across  the  room  seem  blurred.  Look  at  these 
latter ;  they  become  sharply  outlined,  but  the  outline  of  the  finger 
becomes  indistinct.  Notice  that  in  accommodating  for  the  near 
object  there  is  a  feeling  of  effort.  Cease  looking  at  anything  in  par- 
ticular, and  allow  the  eyes  to  come  to  rest.  They  will  be  found  to  be 
accommodated  for  distant  vision. 

52.  Ask  a  person  to  accommodate  his  eye  for  distant  objects.  Then 
look  at  his  eye  from  the  side,  while  he  adapts  his  vision  to  a  near 


THE   EYE   AND    THE    SENSE   OF   SIGHT 


123 


object  without  moving  the  eyeball ;  the  pupil  and  iris  next  the 
observer  will  be  seen  to  move  forward,  owing  to  the  increased  curva- 
ture of  the  anterior  surface  of  the  lens. 

53.  Movements  of  the  Iris.  —  In  the  preceding  experiment  the  diame- 
ter of  the  pupil  was  smaller  when  the  eye  was  accommodated  for  near 
objects,  but  dilated  on  changing  to  distant  vision.  Close  one  eye, 
and  by  aid  of  a  mirror  observe  the  size  of  the  pupil  of  the  other  eye. 
Then  open  the  closed  eye  ;  tiie  pupil  of  the  other  eye  contracts.  Cover, 
with  the  hands,  another  person's  eyes.  On  suddenly  removing  the 
hands,  the  pupils  are  seen  to  contract. 

5-4.  Astigmatism.  —  Close  one  eye  and  look  at  the  radiating  lines  in 
Fig.  72.  Notice  which  lines,  if  any,  appear  with  the  greatest  black- 
ness and  distinctness.  Try  the  other  eye  ;  do  the  two  eyes  agree  ?  Look 
at  the  concentric  circles  of  Fig.  72.     In  w^hat  portion  of  the  figure,  if 


Fig.  72. 


any,  do  the  lines  appear  clearest?  The  teacher  should  obtain,  from 
an  optician,  one  of  the  charts  commonly  used  in  preliminary  tests  lor 
astigmatism.  With  this  he  can  detect  some  of  the  more  pronounced 
cases  of  this  optical  defect  among  his  pupils.  It  may  happen,  how- 
ever, that  veiy  great  defects  cause  little  disturbance,  since  if  the  two 
eyes  are  astigmatic  on  different  axes,  one  eye  may  correct  the  defect 
of  the  other. 

55.  Xearsight  and  F<n\^igJit.  —  These  are  common  defects,  and 
their  causes  should  be  illustrated  by  use  of  the  apparatus  described 
in  Ex.  50.  If  the  teacher  will  perform  some  of  the  simpler  tests 
for  optical  defects  of  the  eye  (and  almost  any  local  optician  will  loan 
the  necessary  apparatus,  and  give  instructions),  he  may  not  only  inter- 


124  CONSCIOUS   NERVOUS   OPERATIONS 

est  and  instruct  his  pupils,  but  confer  lasting  benefits  upon  some  of 
them  in  showing  them  their  defects,  and  the  means  of  correcting 
them. 

56.  The  Blind  Spot.  —  Close  the  left  eye  and  with  the  right  look 
intently  at  the  cross  in  the  following  diagram  (Fig.  73),  holding  the 
book  about  fifteen  inches  in  front  of  the  eye.     Both  cross  and  circle 


Fig.  73.  — Diagram  to  demonstrate  the  existence  of  the  blind  spot. 

are  seen.  Gradually  bring  the  book  nearer  the  eye ;  at  a  certain 
distance  the  circle  disappears  because  its  image  falls  upon  the 
entrance  of  the  optic  nerve.  Bring  the  book  still  nearer;  the  circle 
reappears. 

57.  Field  of  Acute  Vision.  —  Look  at  a  printed  page  without  moving 
the  eyes  and  observe  how  few  words  can  be  seen  distinctly.  The 
diameter  of  this  field  of  distinct  view  will  probably  be  found  to  be 
about  one  and  one-half  inches.  Wherever  the  image  of  an  object 
falls  outside  the  yellow  spot,  it  is  seen  indistinctly. 

58.  Binocular  Vision.  —  Hold  before  each  eye  a  blackened  tube  of 
pasteboard.  Two  distinct  fields  w'ill  be  seen  on  looking  through  the 
tubes.  Cause  the  tubes  to  converge  at  their  free  ends,  and  the  two 
fields  will  finally  fuse  into  one.  This  position  of  the  two  tubes  repre- 
sents approximately  the  normal  convergence  of  the  two  optical  axes. 
Converge  the  tubes  still  more ;  the  two  fields  reappear,  but  they  are 
crossed.  Look  through  the  tubes  at  near  and  at  far  objects.  It  will 
be  found  that,  in  order  to  have  a  single  field  of  vision,  the  tubes  must 
be  converged  more  for  the  near  objects. 

59.  Close  one  eye,  and,  looking  steadily  ahead,  note  how  much  is 
comprised  in  the  field  of  view.  On  opening  the  eye  the  field  is  con- 
siderably enlarged. 

60.  Holding  the  forefinger  six  or  eight  inches  in  front  of  the  nose, 
look  at  a  distant  object,  as  a  tree.  The  forefinger  appears  double. 
Now  accommodate  the  eyes  for  the  finger ;  the  tree  appears  double. 
An  explanation  of  this  can  be  deduced  from  Ex.  58. 

61.  Movements  of  the  Eye.  —  Close  one  eye,  and,  holding  the  finger 
tip  on  the  lid,  feel  the  movements  of  that  eye  as  the  other  eye  looks 
about  in  various  directions. 


THE   EYE   AND   THE    SENSE    OF   SIGHT  125 

62.  Duration  of  Sight  Sensations.  —  Cause  a  small  wheel  to  revolve 
rapidly;  the  spokes  no  longer  appear  distinct,  but  seem  to  be  thinned 
out  and  fused  together  into  a  semitransparent  membrane.  Spin  a 
top  composed  of  an  angular  piece  of  card  fastened  to  a  suitable  axis. 
It  appear^  circular  instead  of  angular. 

63.  Look  at  a  bright  light  for  a  moment.  Then  close  the  eyes; 
the  image  persists  for  a  short  time. 

64.  Fatigue  of  the  Retina.  After  Images.  —  Look  steadily,  for  one  or 
two  minutes,  at  a  window,  and  then  at  a  plain  light-colored  wall.  An 
image  in  which  the  light  parts  of  the  window  are  dark  and  the  dark 
parts  are  light  will  now  be  seen. 

65.  Complementary  Colors.  —  Look  steadily  at  a  piece  of  red  paper 
and  then  at  a  light  background;  a  light  green  after  image  will  be 
seen.  Repeat,  using  different  colored  papers.  From  dealers  in  kin- 
dergarten supplies  can  be  obtained  packages  of  colored  papers  suitable 
for  this  and  other  experiments  on  color. 

66.  Color  Blindness.  —  The  teacher  frequently  finds  pupils  unable  to 
name  colors  correctly.  This  may  be  due  to  color  blindness,  but  in 
most  cases  is  caused  by  defective  training.  To  make  any  accurate 
tests  of  color  blindness,  the  teacher  should  procure  a  set  of  Holm- 
gren's test  worsteds  (price  $2.50)  and  directions  for  experimenting. 


CHAPTER   IX 


THE  EAR   AND   THE   SENSE   OF  HEARING 


167.  The  ear  is  the  mechanism  by  which  we  hear.  It 
has  three  main  divisions,  called  the  external^  the  middle^ 
and  the  internal  ear  (Fig.  74). 


Endolymphatic 
Duct 

^Saccule 


rHr^^^-^""^  Vettibular 

■^''Tympanic  Passage 

Eustachian  Tube  Fenestra  Rotunda 

Fig.  74. —Diagram  of  the  ear,  showing  relationship  of  its  parts. 

168.  The  External  Ear.  —  The  parts  of  the  external  ear 
are  formed  to  collect  and  conduct  waves  of  sound  to  the 
inner  portions  of  the  auditory  apparatus.  They  are  the 
pinna,  the  external  meatus,  and  the  membrane  of  the  tympa- 
num. The  pinna  is  a  sheet  of  elastic  cartilage  covered 
with  skin,  so  folded  as  to  direct  the  waves  of  sound 
through  the  cartilaginous  tube  of  the  meatus,  which  is 
continuous  with  it,  to  the  membrane  of  the  tymjjanum,  or 
eardrum,   which    closes   the'  end  of  the  passage.      Along 

126 


THE   EAK    AND    THE    SENSE    OF    HEARING 


127 


the  tube  of  the  meatus  are  phiced  the  wax  glands  with 
their  ducts. 

169.  The  Middle  Ear,  or  Tympanum,  is  an  irreguhir  cavity 
in  the  temporal  bone,  lined  with  mucous  membrane  wliich 
is  supplied  with  small  glands.  By  means  of  the  Eusta- 
chian tube,  Avhich  passes  from  the  lower  back  part  to  the 
pharynx,  or  upper  cavity  of  the  throat,  the  tympanum 
communicates  with  the  external  air,  and  so  equalizes  the 
pressure  upon  the  two  sides  of  the  membrane  of  the  tym- 
panum which  separates  the  middle  from  the  external  ear. 

Opposite  the  membrane  of  the  tympanum  are  two 
smaller  openings  into  the  chamber  of  the  inner  ear,  called 
the  7'ound  window  (^fenestra 
rotunda^,  and  the  oval  tvin- 
dow  {^fenestra  ovalis~).  These 
are  closed,  however,  by  thin 
membranes.  Three  small 
bones,  called  the  auditory 
ossicles,  form  a  chain  across 
the  middle  ear  (Figs.  74  and 
75).  The  waZ^eits,  or  hammer, 
is  attached  by  one  end  to  the 
membrane  of  the  tympanum, 
while  the  other  end  articu- 
lates with  the  incus,  or  anvil  bone.  The  incus  articulates 
with  the  third  bone,  the  stapes,  or  stirrup  bone,  at  the  top 
of  its  arch.  The  foot  plate  of  the  stapes  fits  into  the  open- 
ing on  the  inner  side  of  the  tympanum  called  the  oval 
window,  and  is  attached  to  the  membrane  which  closes  it. 
170.  The  Internal  Ear,  or  Labyrinth,  is  the  essential  part 
of  the  organ  of  hearing,  the  others  being  merely  con- 
ductors of  sound  waves.  The  labyrinth  is  an  irregular 
chamber  in  the  rocky  part  of  the  temporal  bone  (Figs.  74 


Fig.  75.  — The  ossicles  of  the  ear. 


128 


CONSCIOUS  NERVOUS   OPERATIONS 


Posterior 

Canal 


Anterior 
Canal 


Fenestra  Ovalis 


Fenestra 
Rotunda 


and  76).  Within  it  lies  a  closed  membranous  sac  called 
the  membranous  labyrinth,  which  foUoAvs  the  windings  of 
the  bony  cavity,  and  whose  parts  receive  names  corre- 
sponding to  the  names  given  to  the  parts  of  the  cavity. 

The  central  part  of  the  labyrinth  is  called  the  vestibule  ; 
it  is  about  one  eighth  of  an  inch  in  diameter.     In  its  walls 

are  the  round  and  oval  win- 
dows already  mentioned. 
The  membranous  vestibule 
is  composed  of  two  bags, 
called  the  utricle  and  the 
saccule,  connected  by  a 
roundabout  passage. 

171.  From  the  utricle 
arise  three  semicircular 
canals,  Iji^i-g  in  the  bony 
passages  of  the  same  name. 
One  of  these  is  horizontal 
when  a  person  stands  up- 
right; the  others  are  vertical  but  at  right  angles  to  each 
other.  Two  of  these  canals  are  united  at  one  end,  so  that 
there  are  but  five  openings  from  the  canals  into  the  vesti- 
bule. Each  canal  has  a  swelling  at  one  end  called  the 
ampulla.  At  those  swellings  fibers  from  the  eighth  cranial 
(auditory)  nerve  pass  from  the  bony  wall  through  the 
membranes  of  the  canals,  firmly  attaching  one  to  the  other. , 
For  the  rest  of  their  course  the  membranous  tubes  are  free, 
or  only  loosely  fastened  by  bands  of  connective  tissue  to 
the  bony  walls. 

172.  The  Cochlea  is  the  third  and  most  complex  division 
of  the  inner  ear.  It  has  much  the  appearance  of  a  snail 
shell  of  two  and  a  half  coils.  A  bony  tube  is  coiled  spirally 
round  a  central  tapering  pillar  of  bone.     Into  this  tube 


Fig.  76. 


The  bony  labyrinth  of  the 
right  ear. 


THE   EAR   AND   THE   SENSE   OF   HEARING 


129 


projects  from  the  central  pillar  a  thin  shelf  of  bone  partly 
dividing  the  tube  into  two  i)arts. 

173.  The  Membranous  Cochlea.  —  From  the  edge  of  the 
bony  shelf  of  the  cochlea  two  membranes  reach  to  the 
opposite  wall  of  tlie  cochlea  and  divide  tlie  cavity  into 
three  spiral  tubes  (Fig.  77).     One  of  these,  the  vestibular 


Fig.  77.— Diagram  of  a  cross  section  of  a  single  coil  of  the  cochlea. 

Showing  the  structures  that  compose  the  organ  of  Corti. 


passage  (^scala  vestibuli^^  communicates  with  the  vesti- 
bule. A  second,  the  tympanic  passage  (^scala  tympani^^ 
has  its  base  against  the  membrane  of  the  round  window. 
At  the  apex  of  the  coil  of  the  cochlea  the  vestibular  and 
tympanic  passages  communicate  with  each  other  (Fig.  74). 
The  middle  passage,  the  membranous  cochlea^  or  cochlear 
macy's  phys.  — 9 


130  CONSCIOUS  NERVOUS   OPERATIONS 

canal,  is  closed  at  its  apex,  but  opens  near  its  base  into  the 
saccule.  In  the  cochlear  canal  is  situated  the  most  deli- 
cate part  of  the  ear,  the  organ  of  Corti. 

174.  Fluids  of  the  Labyrinth.  —  The  bony  canal  of  the 
inner  ear  is  lined  with  a  fine  membrane  which  secretes  a 
thin  fluid,  filling  all  the  spaces  of  the  chamber.  The 
closed  sac  of  the  membranous  labyrinth  also  secretes  a 
fluid  similar  in  composition,  but  containing  less  solid 
matter.  When  the  membrane  of  the  tympanum  is 
thrown  into  vibration,  the  movement  is  communicated  to 
the  fluid  filling  the  bony  labyrinth,  and  then  through 
the  thin  wall  of  the  membranous  labyrinth  to  the  fluid 
inclosed,  and  so  to  the  terminations  of  the  auditory  nerve. 

175.  The  Auditory  Nerve  and  the  End  Organs  for  Hearing.  — 
The  eighth  cranial  nerve  arises  by  two  roots  in  certain 
nerve  centers  of  the  medulla  oblongata.  Its  two  divi- 
sions enter  the  labyrinth  between  the  base  of  the  cochlea 
and  the  vestibule.  One  division,  having  several  branches, 
goes  to  the  vestibule  and  semicircular  canals ;  the  other 
passes  up  through  a  channel  in  the  bony  axis  of  the  coch- 
lea, giving  forth  fibers  on  its  way  to  the  bony  shelf 
described  above.  These  pass  through,  or  come  into  rela- 
tion with  the  spiral  ganglion  and  reach  the  organ  of  Corti. 

176.  The  Organ  of  Corti  (Fig.  77),  within  the  mem- 
branous cochlea,  is  understood  to  contain  the  end  organs 
for  the  discrimination  of  degrees,  variations,  and  qualities 
of  sound.  It  is  composed  of  the  rods  of  Corti  with  adja- 
cent hair  cells  and  supporting  parts.  The  rods  are  pillar- 
like cells  attached  by  an  expanded  foot,  or  base,  to  one  of 
the  membranes  of  the  cochlea  and  ending  in  a  swelling 
called  the  head. 

The  pillars  are  arranged  in  pairs,  of  which  there  are 
from  three  thousand  to  five  thousand,  separated  at  their 


THE   EAR   AND   THE   SENSE   OF   HEARING  131 

bases  but  leaning  toward  each  other  to  form  an  arched 
roof  or  tunnel.  Toward  the  apex  of  the  cochlea  the  rods 
increase  in  length  but  are  more  widely  separated  at  the 
base,  so  that  the  tunnel  becomes  lower  and  wider. 
Against  the  rods  lean  other  cells  called  hair  cells,  which  end 
in  many  long,  hairlike  processes.  Between  the  hair  cells 
lie  certain  elongated  supporting  cells.  The  nerve  fibers 
end  in  fine  branches  between  and  around  the^  hair  cells. 

177.  Path  of  an  Auditory  Impression.  — Sound  waves  pass 
through  the  air  and  fall  upon  the  membrane  of  the  tym- 
panum. In  the  middle  ear  they  travel  partly  through 
air  and  partly  through  solid  bodies  —  membranes  and 
bones,  —  and  in  the  inner  ear  through  fluids  and  mem- 
branes. Vibrations  of  the  membrane  of  the  tympanum 
are  "  damped  "  by  the  ossicles  of  the  middle  ear,  which 
also  receive  and  pass  on  the  auditory  tremors  to  the  mem- 
brane closing  the  oval  window.  These  bones  are  so  closely 
bound  together  that  they  vibrate  as  if  they  were  one,  the 
very  slight  amount  of  play  at  the  articulations  serving  to 
prevent  jar  and  fracture. 

From  the  middle  ear  vibrations  pass  to  the  inner  ear 
through  the  attachment  of  the  stapes  to  the  membrane  of 
the  oval  window.  Movement  of  that  membrane  sets  up 
motion  in  the  fluid  filling  the  cavity.  That,  however, 
would  not  be  possible  (since  the  fluid  is  inelastic  and 
incompressible)  were  not  a  vent  provided  at  the  round 
window.  When  the  stapes  pushes  in  the  membrane  of 
the  oval  window,  that  of  the  round  window  bulges  out- 
ward, and  the  action  agitates  the  whole  body  of  the  fluid 
which  fills  the  bony  labyrinth.  But  the  vibrations  in  the 
fluid  are  also  communicated  to  the  walls  of  the  membra- 
nous labyrinth  which  it  bathes,  and  the  fluid  which  the 
latter  contains  is  thereby  set  in  motion. 


132  CONSCIOUS  NERVOUS   OPERATIONS 

Within  the  swollen  ends  of  the  semicircular  canals,  and 
upon  the  Avails  of  the  utricle  and  the  saccule,  are  project- 
ing ridges  composed  of  especially  modified  cells  of  the 
lining,  between  which  are  spindle-shaped  auditory  cells 
from  which  project  auditory  hairs  into  the  fluid.  At- 
tached to  these  thickened  disks,  or  ridges,  are  minute  hard 
particles,  called  otoliths^  which  serve  to  increase  the  effect 
of  the  vibrations.  The  auditory  vibrations  in  the  fluid 
and  in  the  membranous  walls  of  the  labyrinth  reach  the 
auditory  hairs  and  give,  according  to  the  opinions  of  some 
authors,  the  sensation  of  sound,  or  mere  noise.  A  branch 
of  the  vestibular  division  of  the  auditory  nerve  is  distrib- 
uted to  the  semicircular  canals,  and  when  its  ends  are 
affected  by  the  vibrations  in  the  fluids  of  the  labyrinth 
there  result,  as  is  now  believed,  sensations  other  than 
perception  of  sound. 

178.  The  same  vibrations  pass  at  the  same  time  up  the 
channel  of  the  cochlea  from  below,  affecting  on  their  way 
the  walls  of  the  membranous  cochlea,  and  throwing  into 
vibration  the  fluid  which  they  inclose.  By  the  vibrations 
of  the  fluid  and  the  membrane  the  nerve  endings  in  the 
organ  of  Corti  are  acted  upon  in  such  a  way  as  to  give 
rise  to  auditory  impulses,  resulting  in  perception  of  sound 
quality  —  musical  notes,  harmony,  etc.  The  cochlea  alone 
is  now  regarded  as  concerned  with  hearing,  other  parts 
of  the  inner  ear  with  equilibrium,  etc.  Sound  waves  may 
also  reach  the  auditory  cells  by  transmission  through  the 
bones  of  the  head,  as  when  one  hears  the  ticking  of  a 
Avatch  held  between  the  teeth. 

The  auditory  stimulus  j)asses  from  the  auditory  cells 
by  the  minute  nerve  fibers  to  that  branch  of  the  eighth 
cranial,  or  auditory  nerve,  which  passes  through  the  coch- 
lea and  into  the  medulla   oblongata  (Fig.   78),  whence 


THE   EAR   AND   THE   SENSE   OF   HEARING 


133 


certain   fibers  have  been   traced   to   the   corpora  quaclri- 
gemina,  wliile  others  convey  the  impression  to  the  gray 
matter  of  certain  convolutions 
of   the    temporal   lobe    of   the 
cerebrum. 

179.  Function  of  the  Vestibule 
and  Semicircular  Canals.  —  Much 
research  has  in  recent  years 
been  directed  to  the  part  played 
by  these  portions  of  the  inner 
ear,  but  no  investigator  has  yet 
reached  a  conclusion  which  is 
accepted  in  all  its  details  by  all 
others.  It  is,  however,  gener- 
ally believed  that  these  parts 
have  little,  if  any,  direct  con- 
cern with  the  sense  of  hearing 
and  discriminating  sounds. 
The  nerve  branches  distributed 
here  arise  in  the  brain  from  a 
root  of  the  auditory  nerve  dif- 
ferent from  that  which  sends  nerves  to  the  cochlea.  The 
cerebellum,  from  which  some  of  its  fibers  come,  is  well 
known  to  be  the  great  center  for  coordination  of  muscular 
movement,  and  experiments  seem  to  indicate  that  what  is 
called  the  vestibular  branch  of  the  auditory  nerve,  which 
ends  in  the  vestibule  and  semicircular  canals,  conveys  to 
the  brain  impressions  of  position  and  of  movement  in 
space  which  iiave  to  do  with  the  sense  of  equilibrium. 

180.  Hearing  with  Two  Ears.  —  The  two  organs  and  two 
nerves  of  hearing  convey  to  the  brain,  not  tAvo  sensations, 
but  one.  Bv  means  of  two  ears  we  are  able  to  some 
extent  to  determine  the  locality  from  which  sounds  come, 


Fig.  78.— Diagram  of  the  path 
of  an  auditory  impulse. 

The  impulse  passes  from  the 
auditory  cells  iu  the  ear  to  the  cen- 
ter of  hearing  {An  C)  in  the  tem- 
poral lobe  of  the  cerebrum.  Some 
fibers  pass  to  the  anterior  corpora 
quadrigemina  (Q). 


134  CONSCIOUS  NERVOUS   OPERATIONS 

but  our  judgment  as  to  position  in  space  of  sound-pro- 
ducing bodies,  and  of  directions  of  sound,  are  indirect  and 
not  always  reliable.    * 

181.  Differences  in  Sound  Perception.  — The  ears  of  differ- 
ent persons  vary  greatly  in  power  to  distinguish  differ- 
ences in  sound  and  in  pitch,  or  the  number  of  vibrations 
in  a  given  time.  All  are  limited  in  the  perception  of 
high-pitched  notes.  The  ear  may  become  wearied  in 
respect  to  sound  of  a  particular  pitch,  much  as  the  eye  is 
soon  fatigued  in  respect  to  a  particular  color. 

182.  Care  of  the  Ear.  —  A  cold  which  causes  inflamma- 
tion of  the  throat  often  affects  the  lining  membrane  of 
the  Eustachian  tube  and  that  of  the  middle  ear,  causing 
temporary  partial  deafness.  If  the  cause  often  recurs, 
one  or  both  ears  may  be  permanently  impaired.  Some- 
times repeated  attacks  of  inflammation  in  the  ear  —  as 
from  abscesses  —  result  in  perforation  of  the  membrane 
of  the  tympanum  and  great  injury  to  the  hearing. 

Generally  the  wax  which  is  secreted  in  the  external 
canal  of  the  ear  needs  no  attention,  and  should  not  be 
picked  out.  Occasionally,  hoAvever,  it  accumulates  and 
hardens  upon  the  membrane  of  the  tympanum  so  as  to 
interfere  with  its  vibrations  and  impair  the  hearing.  In 
such  a  case  it  should  be  removed  by  a  surgeon. 

Warm  or  tepid  water  should  be  used  for  washing  the 
ears  —  never  very  cold  water.  Before  going  to  baths 
in  cold  water  or  in  salt  water  the  ears  should  be  filled 
with  soft  absorbent  cotton. 

A  sudden  very  loud  noise,  as  from  a  gun  or  cannon, 
has  been  known  to  rupture  the  eardrum,  and  a  sudden 
shout  close  to  a  child's  ear  has  been  known  to  make  it 
deaf.  Insects  sometimes  crawl  into  the  canal  of  the  ear, 
in  spite    of   the    Avax  and  the  hairs  there  Avhich  usually 


THE   EAR  AND   THE   SENSE   OF   HEARING  135 

prevent  such  accidents.     They  do  not  often  do  harm,  and 
may  be  removed  by  dropping  warm  water  into  the  ear. 

Demonstrations  and  Experiments 

67.  Dissection  of  the  Ear.  —  The  external  and  the  middle  ear  can  be 
very  easily  studied  by  making  a  dissection  of  the  head  of  a  cat  or 
other  domestic  animal.  Remove  the  lower  jaw,  expose  and  open  the 
temporal  bulla.  The  latter  is  in  many  animals  a  conspicuous  rounded 
protuberance  near  the  articulation  of  the  jaw.  The  tympanic  cavity 
with  the  contained  ossicles,  etc.,  can  then  be  studied.  The  internal  ear 
cannot  be  easily  examined  because  of  its  smallness  and  well-nigh  in- 
accessible situation  in  the  rocky  portion  of  the  temporal  bone.  The 
bone  which  contains  it  can  be  dissected  out,  and  the  general  outlines 
of  the  cochlear  region  discerned.  Or,  this  portion  of  the  skull  may 
be  treated  with  weak  solution  of  muriatic  acid  for  some  days,  after 
which  the  parts  may  be  partly  dissected  out. 

68.  Effect  of  Varying  A  ir  Tension  in  the  Tympaiium.  —  AVhile  listening 
to  a  ticking  watch,  close  both  nose  and  mouth,  and  expel  as  much  air 
as  possible  from  the  lungs,  thus  forcing  the  air  through  the  Eustachian 
tube  into  the  middle  ear.  The  ticking  sounds  fainter.  Or  under  like 
conditions  inhale  as  much  as  possible.     The  result  is  as  before. 

69.  Judgment  of  the  Direction  of  Sounds.  —  Let  a  pupil,  seated,  keep 
his  eyes  closed.  Clink  together  two  coins  at  varying  distances  and 
directions  from  his  head,  and  require  him  to  indicate  the  direction  of 
the  sound.  Observe  that  while  he  rarely  fails  to  distinguish  between 
right  and  left,  he  often  errs  in  respect  to  other  directions.  Have  him 
hold  his  hands  vertically  one  in  front  of  each  ear,  and  see  if  his  judg- 
ment of  direction  is  thereby  altered.  Close  one  of  his  ears  with 
absorbent  cotton,  and  try  the  effect  upon  his  location  of  sounds. 

70.  Auditory  Fatigue.  —  Strike  a  tuning  fork,  press  the  stem  down 
upon  the  crown  of  the  head,  and  hold  it  there  until  the  sound  dies 
away.  Then  remove  it,  and  after  a  short  interval  replace  it.  The 
sound  will  be  heard  again,  but  very  faintly. 


CHAPTER    X 


THE  VOCAL  APPARATUS 


183.  The  Larynx,  which  contains  the  vocal  cords^  is  the 
special  voice  organ.  It  is  a  chamber  made  up  of  cartilages, 
membranes,  and  muscles.  Four  cartilages  compose  the 
framework.  The  thyroid  is  the  largest,  and  forms  a 
prominent  ridge  in 
front  (called  "  Ad- 
am's apple  ")  with 
broad,  flat  sheets  at 
the  sides,  ending  in 
prolonged  angles, 
above  and  below 
(Figs.  79  and  80). 
It  does  not  meet  at 
the  back  of  the  lar- 
ynx. The  cricoid  car- 
tilage^ on  the  other 
hand,  is  a  complete 
ring,  the  back  being 
much  wider  than  the 
front.  On  top  of  the  broad  hinder  portion  of  the  cricoid 
are  the  small,  triangular  arytenoid  cartilages,  which  form 
with  the  cricoid  a  true  joint,  having  synovial  membrane 
and  ligaments  (Fig.  81). 

Besides   these   four  principal    cartilages,  which  are    of 
hyaline,  or  nonfibrous  cartilage,  there  are  five   others  of 

136 


Trachea 


Fig.  79.  — Front  (ven 
tral)  view  of  larynx. 


Trachea 

Fig.  80.  — Side  view 
of  larynx. 


THE   VOCAL   APPARATUS 


13T 


Fig.  81— Cartilages  of 
larynx,  back  (dorsal) 
view. 


3'ellow  fibrocartilage.  They  are  the  epiglottis,  which  is 
attached  to  the  upper  front  part  of  the  larynx  and 
forms  a  lid  to  the  chamber  ;  the 
cartilages  of  Santorini,  little  horn- 
shaped  projections  perched  on  top 
of  the  arytenoids ;  and  the  carti- 
lages of  Weisberg,  which  are  still 
smaller  bits  of  cartilage  lying  in 
folds  of  the  mucous  membrane  in 
the  sides  of  the  upper  membranous 
lining  of  the  larynx. 

A  sheet  of  membrane  connects 
the  thyroid  cartilage  with  the  hyoid 
bone  at  the  root  of  the  tongue  (Figs. 
79  and  80).  The  thyroid  is  also  joined  to  the  cricoid  by 
joints  with  svnoA'ial  membrane,  and  the  lower  projections, 
or  horns,  of  the  thyroid  clasp  the  cricoid  closely,  though 
permitting  movement  between  them.  The  cricoid  is  at- 
tached by  membrane  to  the  upper  cartilaginous  ring  of  the 
trachea,  or  windpipe.  These  parts,  with  the  many  small 
muscles  and  ligaments  attached,  form  the  vocal  apparatus. 

184.  The  larynx  is  flattened  behind,  where  it  closely 
adheres  to  the  esophagus  (Fig.  82).  The  esophagus  is 
the  muscular  tube  which  conveys  food  and  drink  from  the 
mouth  to  the  stomach.  Its  enlarged  upper  portion  is 
called  the  pharynx,  and  lies  back  of  the  cavity  of  the 
mouth.  The  larynx  lies  below  and  in  front  of  the 
pharvnx.  In  ordinary  respiration  the  epiglottis  stands 
nearly  erect,  leaving  open  the  glottis,  or  passage  into  the 
larynx.  In  the  process  of  swallowing,  the  epiglottis  is 
pressed  backward  and  downward,  closing  the  glottis  and 
permitting  the  food  to  slide  down  the  esophagus  instead 
of  dropping  into  the  windpipe. 


138 


CONSCIOUS   NERVOUS   OPERATIONS 


185.  The  Vocal  Cords.  —  The  larynx  is  smoothly  Imed 
with  mucous  membrane  except  where  it  narrows  at  the 
glottis.  Here  at  the  base  of  the  epiglottis  are  seen,  first, 
on  each  side  of  the  lining  membrane,  ridges  called  false 
vocal  cords,  which  are  not  concerned  in  speech  (Fig.  82). 
They  play  the  chief  part  in  closure  of  the  glottis  during 
expiration.     A  little  below  them  are  the  true  vocal  cords, 


opening  of 
Eustachian  tube 


Soft  palate  — -2 


Hard  palate 


Tongue 


Hyoid  bone 
False  vocal  cords 


True  vocal  cords 


Thyroid  carti- 
lage 

Cricoid  carti- 
lage 


—  Vertical  section  of  the  head  and  neck. 


thickened  bands  of  elastic  tissue  running  in  the  mucous 
membrane  from  the  front  angle  of  the  thyroid  cartilage 
backward  to  their  attachment  at  the  base  of  the  arytenoid 
cartilages.  Between  the  true  and  the  false  vocal  cords  is,  on 
each  side,  a  recess  called  the  ventricle.  The  true  vocal  cords 
have  fine,  smooth  edges,  and  are  shining  white  in  color. 

186.   The  Glottis.  —  In  ordinary  respiration  the  glottis  is 
a  triangular  opening  with  its  apex  in  front.     In  deep  or 


THE    VOCAL    APPARATUS  139 

labored  breatliing  it  widens  during  inspiration  and  narrows 
during  expiration. 

187.  Vocalization.  —  There  may  be  a  sort  of  speech  with- 
out the  aition  of  the  larynx  or  the  vocal  cords,  when  the 
muscles  of  respiration,  the  lips,  and  what  are  called  the 
resonating  cavities  above  the  larynx  are  alone  brought  into 
play.  This  produces  whis].H'ri}u/.  But  for  vocalization 
the  vociil  cords  must  l:>e  brought  very  near  together,  made 
tense  and  parallel,  and  a  current  of  air  must  be  forced 
smftly  through  the  narrow  slit,  throwing  them  into  rapid 
vibration.  This  is  effected  by  means  of  a  complicated 
arrangement  of  muscles  and  ligaments  attached  to  the 
various  cartilages.  The  two  inner  angles  of  the  arytenoid 
cartilages  are  drawn  together  by  the  contraction  of  certain 
muscles,  while  others  contract  to  stretch  the  vocal  cords. 
The  thyroid  and  cricoid  cartilages  move  upon  each  other 
to  assist  in  the  process.  The  muscles  of  the  thorax  and 
the  abdomen  are  also  brought  into  special  action,  and  the 
column  of  air  in  the  air  chamber  composed  of  the  trachea 
and  the  bronchial  system  is  thrown  into  vibration.  Sound 
is  a  result  of  the  whole  process. 

188.  The  Resonating  Cavities  (Fig.  82).  —  The  pharynx, 
the  mouth,  and  the  nasal  cliambers  are  resoriating  cavities, 
which,  by  very  slight  changes  in  form  and  size,  are  able 
to  bring  into  special  prominence  different  parts  of  the 
general  tone  produced  in  the  larynx,  and  so  modify  the 
resulting  sound. 

189.  Speech  is  the  enunciation  of  articulate  sounds  to 
express  thought,  and  is  the  result  of  the  action  of  the  vol- 
untary muscles  by  which  the  vibrations  produced  in  the 
larynx  are  modified  in  the  resonating  cavities.  The  fac- 
ulty of  speech  is  a  distinctive  gift  of  man,  and  is  possessed 
by  no  other  animal.     It  is  a  natural  gift,  bttt  its  use  is  the 


140  CONSCIOUS  NERVOUS   OPERATIONS 

result  of  training,  and  skill  is  acquired  only  by  long  years 
of  practice.  The  complex  and  greatly  varied  action 
required  in  speech  may  take  place  with  great  rapidity, 
and  may  be  continued  for  hours  without  exhaustion,  as  in 
the  case  of  an  accomplished  singer  or  public  speaker. 

190.  Vowels  and  Consonants.  —  Voice  becomes  speech 
through  the  modifying  action  of  the  lips,  tongue,  throat, 
etc.  Those  sounds  of  the  spoken  alphabet  which  require 
the  more  open  mouth,  the  more  resonant  and  more  pro- 
longed tone,  are  called  vowels;  those  which  are  uttered 
with  the  closer  position,  and  are  less  prolonged  and  less 
resonant,  are  called  consonants.  Compare  the  position  of 
the  parts  of  the  mouth  in  enunciating  the  a  in  far  with 
that  in  sounding  the  h  in  cah^  for  example.  Between 
vowels '  and  consonants  there  is  no  absolute  division. 
Sounds  represented  by  some  of  the  letters  are  more  open 
in  some  words  or  syllables  than  in  others.  Thus,  I  and 
n  are  sometimes  vowels  and  sometimes  consonants. 

191.  duality  of  Voice.  —  Voices  are  spoken  of  as  "soft," 
"  harsh,"  ''  rasping,"  "  rough,"  "  sweet,"  "  low,"  "  gentle," 
etc.  An  agreeable  voice  is  a  most  attractive  characteris- 
tic and  a  most  desirable  possession.  As  the  vocal  appa- 
ratus is  wholly  under  the  control  of  the  will,  and  as  its  use 
is  chiefly  a  matter  of  imitation,  it  is  of  great  importance 
that  while  the  habit  of  speech  is  forming  the  young  should 
be  associated  with  those  whose  vocal  habits  are  agreeable 
and  refined,  and  that  the  attention  of  children  should  be 
early  directed  to  the  cultivation  of  soft  and  pleasant  tones 
of  voice.  In  this  respect  Americans  are  especially  negli- 
gent, and  "  the  American  voice  "  has  become  a  byword 
and  a  reproach  in  Europe. 

192.  Musical  Sounds.  —  Sounds  produced  by  regular  vibra- 
tions are  musical.      Irregular  vibrations  result  in  noise. 


THE   VOCAL   APPARATUS  141 

No  sharp  line  of  separation  can,  however,  be  drawn.  The 
sounds  of  ordinary  speech  are  due  to  regular  vibrations, 
and  are  hence  musical. 

193.  Pitch  depends  upon  the  rapidity  of  the  vibrations, 
and  that  varies  with  the  length  of  the  cords  and  with 
their  tension.  In  women  the  vocal  cords  are  shorter  than 
in  men,  and  the  voice  is  an  octave  higher  in  pitch.  Pitch 
due  to  tension  of  the  cords  is  a  matter  of  voluntary  con- 
trol within  the  range  of  a  voice.  Loudness  depends  upon 
the  force  of  expiration.  Stammering  is  due  to  lack  of 
coordination  in  the  muscles  of  speech. 

194.  Nervous  Mechanism  of  the  Larynx.  —  A  certain  area 
in  the  left  hemisphere  of  the  cerebrum  is  recognized  as  the 
nervous  center  in  which  impulses  resulting  in  speech  origi- 
nate. From  the  cells  of  this  center  nerve  fibers  run  to 
other  cells  in  the  wall  of  the  foui'th  ventricle  of  the  brain, 
to  the  medulla  oblongata,  and  on  into  the  spinal  cord.  By 
means  of  these  communicating  fibers  the  center  for  speech 
is  brought  into  connection  with  other  groups  of  nerve 
cells,  from  which  arise  the  various  nerves  which  are  con- 
cerned in  vocalization.  These  are  very  numerous,  for  the 
muscles  of  the  face,  the  tongue,  the  thorax,  and  the  abdo- 
men, as  well  as  those  of  the  larynx,  are  called  into  action  in 
speaking,  singing,  etc.  Those  nerves  distributed  to  the 
muscles  of  the  larynx  are  branches  of  the  vagus,  or  pneu- 
mogastrie,  which  is  the  tenth  cranial  nerve  and  rises  from 
the  medulla  oblongata. 

Suppose  there  arises  in  a  man's  mind  a  thought  which 
he  desires  to  express  in  audible  speech.  He  remembers 
the  sounds  of  the  words  Avhich  Avill  serve  his  purpose,  and 
impulses  arise  in  that  part  of  the  speech  center  called  the 
auditory  ivord  center^  from  which  they  pass  to  the  motor 
center.     Thence  the   nerves    of  the  various   parts  of  the 


142 


CONSCIOUS   NERVOUS   OPERATIONS 


vocal  apparatus  distribute  the  impulse  to  the  necessary 
muscles.  In  reading  aloud  it  is  the  end  organs  for  vision, 
the  eyes,  which  are  first  stimulated  (Fig.  83);  then  the 
impulse  is  carried  to  the  visual  center  in  the  brain,  from 

which  nervous  influences  travel 
by  connecting  nerve  fibers  to 
the  auditory  word  center. 
There,  as  before,  the  sound  of 
the  words  is  revived  and  the 
impulse  follows  the  path  previ- 
ously described. 

195.  —  When  a  person  writes 
from  dictation,  another  course 
is  followed  (Fig.  84).  The 
auditory  end  organs  of  the 
inner  ear  are  first  stimulated; 
the  impression  travels  hy  the 
auditory  nerves  to  the  audi- 
tory word  center,  then  across 
to  the  visual  word  center, 
reviving  there  the  appearance 
of  the  words.  Impulses  pass 
thence  to  the  motor  centers 
and  by  motor  nerves  to  the 
various  muscles  of  the  arm 
and  hand  involved  in  writing. 
If  nerve  fibers  which  connect 
the  two  word  centers,  visual 
and  auditory,  are  diseased,  nei- 
ther reading  aloud  nor  writing  from  dictation  is  possible. 
Vocalization  may  also  be  the  result  of  reflex  nervous 
action,  as  when  an  involuntary  scream  follows  sudden 
fright. 


Fig.  83.  — Diagram  of  path  of 
nervous  impulses  in  reading 
aloud.     - 

Au  C  hearing  center. 

OC     sight  center. 

Sp  C  speech  center  in  left  hemi- 
sphere. 

V,  VII,  X,  XI,  XII,  Sp  iV  nerves 
supplying  motor  fihers  to  the 
speecli  organs:  lips,  tongue, 
chest,  etc. 


THE   VOCAL   APPARATUS 


143 


196.  Dumbness  is  most  frequently  due  to  deafness.  The 
auditory  word  center  has  never  been  stimulated.  In 
recent  years  it  has  been  found 
possible  to  stimulate  the  speech 
center  tln-ough  its  connection 
with  the  visual  center.  Chil- 
dren born  deaf  are  taught  to 
imitate  the  movements  of  the 
mouth,  tongue,  and  throat  of 
one  who  speaks,  and  speech 
results  from  these  remembered 
movements  acting  upon  the 
speech  center. 

197.  Care  of  Throat  and  Voice. 
—  If  the  delicate  lining  mem- 
brane of  the  larynx  becomes  in- 
flamed through  "  taking  cold  '* 
or  from  exposure  to  dust  or 
irritating  gases  or  from  over- 
use or  strain  of  the  vocal 
cords,  the  voice  is  injured  and    pig.  84.  — Diagram  of  the  path 

its    use    may    become    painful       o^  the  nervous  impulses  in 

•^  ^  writing  from  dictation, 

or   impossible.      These    causes  .lu  c  ceuter  of  hearing. 

should  be  avoided.  When  a 
daily  cold  bath  is  not  practi- 
cable, a  dash  of  cold  water  over  the  neck  on  rising  in 
the  morning  will  prove  a  tonic  for  the  throat  and  help 
to  avert  colds,  hoarseness,  and  sore  throat.  Breathing 
should  be  through  the  nose,  and  not  through  the  mouth, 
and  children  should  be  trained  in  infancy  to  sleep  with 
the  mouth  closed.  In  going  from  the  warm  air  of  the 
house  into  the  cold  outer  air  in  winter  the  precaution 
of  closing  the  mouth  is  especially  to  be  observed.     Pass- 


MC  motor  center. 
OC   sia:ht  center. 


144  CONSCIOUS   NERVOUS   OPERATIONS 

ing  through  the  winding  nasal  canal,  the  air  becomes 
tempered  before  reaching  the  sensitive  membranes  of 
throat  and  lungs;  also  much  of  the  dust  always  present  in 
the  atmosphere  is  caught  by  the  moist  mucous  lining  of 
the  nostrils,  and  the  deeper  air  passages  are  protected. 

It  is  not  necessary,  in  order  to  avoid  cold,  that  the 
throat  should  be  thickly  swathed  in  wraps  of  wool  and 
fur.  Too  much  clothing  about  the  neck  causes  excess  of 
perspiration  there  and  makes  the  parts  weak  and  tender. 

198.  Special  Training  of  the  voice  for  singing  or  public 
speaking  should  not  be  begun  by  either  boys  or  girls 
before  the  age  of  sixteen  or  seventeen,  and  should  always 
be  attended  with  judgment  and  care  against  overstrain. 

199.  Alcohol  and  Tobacco  as  affecting  the  Vocal  Organs. 
—  As  the  perfect  control  of  the  voice  depends  upon  the 
healthy  condition  of  all  the  muscles  connected  with  the 
vocal  apparatus,  and  upon  the  accurate  adjustment  of 
nervous  force  to  their  varying  needs,  anything  which 
affects  those  muscles  or  the  nerves  affects  also  the  voice. 
Alcohol  and  tobacco  do  affect  both.  The  mucous  mem- 
brane of  the  larynx  is  often  much  inflamed  by  tobacco 
smoking,  and  especially  by  the  use  of  cigarettes.  The 
inflammation  may  extend  through  the  Eustachian  tubes, 
impairing  the  hearing,  and  into  the  bronchial  tubes,  caus- 
ing an  annoying  cough.  A  disease  known  as  "smoker's 
sore  throat "  may  result.  Alcoholic  beverages  irritate  the 
throat  and  are  often  forbidden  to  those  cultivating  the 
voice  for  singing. 

Demonstration 

71.  Dissection  of  the  Larynx.  —  At  a  slaughterhouse  can  be  obtained 
a  trachea  of  an  ox  with  the  larynx  intact  and  a  portion  of  the  esoph- 
agus;  the  hyoid  bone  may  be  present  also.  With  this  material  the 
principal  topics  of  this  chapter  can  be  illustrated. 


PART    III 

NERVOUS  OPERATIONS  UNCONNECTED  WITH 

CONSCIOUSNESS 

Those  nervous  operations  of  which  man  is  necessarily 
conscious  and  which  are  directly  concerned  in  his  useful- 
ness and  happiness,  cannot  continue  to  minister  to  his 
higher  nature  without  the  assistance  of  another  set  of 
actions  of  which  he  is  in  health  almost  wholly  uncon- 
scious. The  complicated  mechanisms  for  producing  sen- 
sation and  voluntary  motion  are  constantly  worn  away  at 
every  point,  and  every  tissue  must  be  as  constantly  re- 
newed. Through  the  action,  at  every  moment  of  life,  of 
nerves  and  nerve  cells  whose  office  it  is  to  preside  over 
what  are  called  the  vital  processes,  the  body  is  kept  in 
condition  for  the  exercise  of  its  conscious  powers.  Those 
vital  processes  are  included  under  the  general  term  nutri- 
tion^ that  is,  the  growth,  waste,  and  repair  of  tissue. 
Nutrition  is  effected  by  means  of  the  circulation  of  the 
blood,  digestion  (including  absorption  and  assimilation}, 
respiration,  and  excretion.  Because  these  operations  are 
wholly  dependent  upon  nervous  influences,  and  because 
they  go  on  through  life  without  necessary  connection 
with  consciousness,  they  are  grouped  here  as  unconscious 
nervous  operations. 


145 


Fig.  85.  — The  chief 
blood  vessels. 


CHAPTER   XI 

BLOOD,   LYMPH,   AND   CHYLE 

200.  Function  of  the  Blood.  —  It  will  be  remembered  that 
one  of  the  essential  properties  of  the  living  cell  is  its 
power  to  incorporate  into  its  own  substance  matter  from 
outside  itself,  a  process  which  results  in  growth  or  in 
repairing  waste ;  while  another  property,  involved  in 
this,  is  the  power  to  break  down  by  oxidation,  that  is,  to 
resolve  portions  of  its  own  body  into  simpler  chemical 
substances,  thus  producing  waste  matter. 

In  order  that  this  double  process  may  go  on  continually 
(as  it  must  while  the  cell  is  living),  oxygen  and  oxidizable 
substances,  that  is,  food,  must  be  brought  to  each  cell,  and 
provision  must  be  made  for  removing  the  waste  products. 
The  blood  is  the  medium  for  accomplishing  this. 

201.  The  Blood  as  a  Tissue. —  Blood  is  classed,  for  valid 
reasons,  among  the  connective  tissues.  While  it  does  not 
furnish  support  to  the  body  or  its  parts  in  the  same  sense 
as  do  more  solid  connective  tissues,  —  such  as  bone  or 
cartilage,  —  it  does  support  the  whole  body  by  conveying 
nutriment  to  every  part.  It  is  like  other  connective 
tissues  also  in  that  the  cells  make  up  a  comparatively 
small  portion  of  its  substance,  the  intercellular  material 
being  largely  in  excess.  And,  finally,  it  is  formed  in  the 
development  of  the  embryo  from  the  same  layer  as  are 
the  other  connective 'tissues. 

macy's  phys.  — 10  147 


148  UNCONSCIOUS  NERVOUS   OPERATIONS 

202 .  Structure  of  the  Blood.  —  Under  the  microscope  the 
blood  is  seen  to  consist  of  a  nearly  colorless  fluid,  the 
plasma^  in  which  float  cells  of  two  sorts,  called  from  their 
color  the  red  and  the  white  (or  colorless)  corpuscles  (Fig. 
17,  p.  26).  Ordinarily  there  are  several  hundreds  of  red 
corpuscles  to  one  of  the  white  corpuscles,  and  to  them  the 
color  of  the  blood  is  due. 

203.  The  Quantity  of  Blood  in  the  human  body  is  esti- 
mated at  about  one  thirteenth  tlie  body's  total  weight,  or, 
in  a  person  of  average  size,  about  one  and  a  quarter 
gallons.  Any  deficiency  of  blood  in  the  body  (as  from 
hemorrhage),  is  soon  supplied  by  the  passage  of  water 
from  the  tissues  to  the  blood  by  means  of  the  lymph 
(§  209),  and  an  excess  is  removed  by  the  transfer  of 
water  to  the  tissues,  and  by  the  secretion  of  the  kidneys. 
Thus  the  quantity  of  blood  in  the  system  is  practically 
invariable. 

204.  The  Red  Corpuscles  are  unnucleated  cells,  all  of 
nearly  the  same  size  —  about  3 2^0^  ^^  ^^^  i^^^  "^  diameter, 
and  one  fourth  of  that  in  thickness.  They  are  round  and 
flat,  but  slightly  thicker  at  the  edge  than  in  the  middle. 
Being  flexible  and  elastic  they  are  bent  out  of  shape  as 
they  are  crowded  together  in  the  current,  but  resume 
their  usual  form  when  the  pressure  is  removed.  They 
have  a  close,  colorless,  spongy  framework,  —  the  stroma^  — 
while  by  far  the  larger  part  of  their  substance  is  a  red 
coloring  matter  in  the  meshes  of  the  stroma,  called  hemo- 
globin. This  is  the  useful  part  of  the  corpuscle,  the 
stroma  apparently  having  only  the  office  of  holding  the 
hemoglobin  in  convenient  shape. 

205.  The  Formation  of  the  Red  Corpuscles  is  found  to  take 
place  in  the  red  marrow  of  the  bones.  The  peculiar  tissue 
called  red  marrow  is  richly  supplied  with  blood  vessels 


BLOOD,   LYMPH,    AND   CHYLE  149 

having  very  thin  walls.  Within  these  vessels  are  found 
colored  nucleated  cells,  some  of  which  become  changed  in 
the  marrow  into  unnucleated  red  disks  which  are  swept 
into  the  blood  current.  It  is  the  important  function  of 
the  red  corpuscles  to  take  in  oxygen  from  the  air  which 
reaches  the  blood  in  the  lungs,  and  carry  it  to  the  other 
tissues  of  the  body.  The  red  corpuscle  lives  in  the  blood 
for  an  unknown  time.  When  it  dies,  a  new  one  takes 
its  place.  The  spleen  also  is  believed  to  aid  in  the  manu- 
facture of  both  the  red  corpuscles  and  the  white,  but  we 
have  little  positive  knowledge  upon  the  subject. 

206.  The  White  Corpuscles  are  mostly  larger  than  the 
red,  being  generally  about  -g-^oo"  ^^  ^^^  ^^^^-'^  ^^^  diameter, 
though  some  are  smaller  than  the  red.  Some  are  globular 
masses  of  granular  protoplasm  without  cell  walls  and  hav- 
ing one  or  more  nuclei.  Others  are  of  irregular  and  con- 
stantly changing  shape,  less  granular  than  the  first  and 
with  several  nuclei.  Many  writers  have  remarked  the 
striking  likeness  of  these  corpuscles  to  the  one-celled 
animalcule,  the  amoeba.  They  have  the  same  power  as 
the  amoeba  to  change  their  shape  spontaneously,  sending 
out  processes  from  various  parts  of  their  circumference; 
and  they  are  able  to  take  in  and  digest  the  bacilli  Avhich 
are  sometimes  found  in  the  blood,  as  the  amoeba  digests 
food.  There  are  found  in  the  blood  some  other  small 
bodies,  whose  nature  and  purpose  are  unknown. 

207.  Chemical  Composition  of  Blood.  —  The  blood  is  alka- 
line, owing  to  the  presence  of  small  quantities  of  alkaline 
salts.  It  contains  chlorides,  phosphates,  and  carbonates 
of  sodium  and  potassium,  and  smaller  quantities  of  cal- 
cium and  magnesium. 

208.  Clotting  of  the  Blood.  —  The  blood  in  the  blood  ves- 
sels is  perfectly  fluid,  but  if  drawn  out  and  allowed  to 


150       UNCONSCIOUS  NERVOUS  OPERATIONS 

stand  for  a  few  minutes,  it  becomes  a  firm  mass  of  jelly. 
After  an  hour  or  more,  a  yellow  fluid,  called  serum,  begins 
to  ooze  from  the  clot,  which  shrinks  in  size.  The  clotting 
is  caused  by  the  formation,  in  the  liquid  blood,  of  a  close 
network  of  fine  fibrils,  called  fibrin,  in  which  the  corpus- " 
cles  of  both  kinds  are  entangled,  while  serum  is  the  plasma 
of  the  blood,  minus  an  element  in  its  composition  called 
fibrinogen,  which  changes  into  the  solid  fibrin  in  the  coag- 
ulation. It  is  thought  that  when  the  blood  leaves  the 
blood  vessel,  or  in  some  way  comes  in  contact  with  foreign 
matter,  a  portion  of  the  white  corpuscles  are  broken  up, 
and  thus  is  set  free  a  peculiar  substance  called  fibrin  fer- 
ment. It  is  this  which  acts  upon  the  fibrinogen,  and 
causes  it  to  become  fibrin.  The  fibrin  may  be  gotten  out 
from  a  quantity  of  freshly  drawn  blood  by  quickly  stir- 
ring or  Avhipping  it  with  a  bunch  of  twigs.  The  tiny 
white  threads  cling  to  the  sticks,  and  by  washing  in- water 
may  be  freed  from  the  few  entangled  corpuscles  which 
remain,  leaving  the  fibrin  pure. 

This  power  which  the  blood  has  to  clot  is  of  great 
value,  since  by  its  means  small  breakages  in  or  injuries  to 
the  innumerable  tubes  conveying  the  blood  throughout 
the  system  are  quickly  stopped,  and  the  serious  hemor- 
rhage which  would  otherwise  result  is  quickly  checked, 
while  the  ruptured  wall  of  the  blood  vessel  is  given  time 
to  heal. 

209.  Lymph.  —  It  is  by  the  blood  that  nutriment  is  car- 
ried to  every  part  of  the  body;  but  the  blood  is  always 
inclosed  within  the  walls  of  the  tubes  called  blood  vessels, 
and,  as  blood,  does  not  come  in  contact  with  the  cells  of 
the  tissues. 

In  the  capillaries,  which  are  the  finest  ramifications  of 
the  blood  vessels,  some  of   the  plasma  passes  from  the 


BLOOD,    LYMPH,    AND    CHYLE  151 

blood  through  the  walls  of  the  vessels  into  the  spaces 
between  those  walls  and  the  substance  of  the  tissues 
around.  This  fluid  is  called  lymph  and  is  that  which 
nourishes  the  tissue  elements.  It  is  clear,  nearly  trans- 
parent, and  contains  more  water  Avith  less  solid  matter 
than  the  plasma  of  the  blood.  White  corpuscles  similar 
to  those  in  the  blood  are  found  in  it,  and,  like  the  blood, 
it  coagulates  by  the  formation  of  fibrin.  Like  the  blood, 
also,  lymph  is  conveyed  from  the  tissues  in  tubes,  the 
lympliatics  or  lymphatic  vessels,  which  finally  join  the  great 
blood  vessels,  and  so  return  to  the  blood  the  substances 
drawn  from  it  in  the  capillaries. 

210.  Lacteals  and  Chyle.  —  The  lymphatics  of  the  small 
intestine  are  called  lacteals ;  after  a  meal  containing  fat, 
they  convey,  instead  of  clear  lymph,  a  milky  fluid  which 
is  called  chyle,  and  is  a  product  of  digestion. 

Experiments 

72.  Blood  Corpuftclea.  —  Prick  the  finger  with  a  sterilized  needle, 
mount  the  di'op  of  blood  thus  obtained,  and  examine  it  with  both  low 
and  high  powers  of  the  compound  microscope.  There  will  be  seen 
large  numbers  of  round  bodies  of  a  faint  red  tint  —  the  red  cor- 
puscles. These  are  seen  to  be  small  disks,  and  appear  dumb-bell 
shaped  when  viewed  on  edge,  owing  to  their  being  thinner  in  the 
center  than  on  the  edges.  Occasionally  among  the  red  corpuscles 
may  be  seen  slightly  larger,  transparent,  sometimes  irregular,  bodies  — 
the  white  or  colorless  corpuscles.  If  watched  for  some  time,  they  will 
probably  show  slight  changes  in  shape. 

73.  Clotting  of  Blood.  — At  a  slaughterhouse  fresh  blood  can  be 
obtained.  If  it  be  sthred  vigorously  immediately  after  being  drawn 
from  the  blood  vessels,  the  fibrin  can  be  separated  from  the  blood 
serum  and  corpuscles.  Blood  allowed  to  stand  after  being  drawn 
shows  a  firm  clot.  Both  '"whipped"  blood  and  fibrin  and  the  clotted 
blood  should  be  examined  by  the  pupils. 

The  clotting  of  blood  may  be  prevented  by  adding  to  it,  as  it  is 


152  UNCONSCIOUS   NERVOUS   OPERATIONS 

drawn  from  the  blood  vessels,  about  one  fourth  its  volume  of  a  satu- 
rated solution  of  sulphate  of  magnesia.  This  "  salted  "  blood  may  be 
kept  in  a  cool  place  for  several  days  without  clotting.  It  may  be 
made  to  clot  by  diluting  it  with  five  to  ten  times  its  volume  of  water. 

A  more  satisfactory  method  of  preventing  the  clotting  of  blood,  the 
writer  has  found,  consists  in  adding  oxalate  of  potash  in  the  propor- 
tion of  one  part  of  a  5  per  cent  solution  of  oxalate  of  potash  to 
twenty-five  parts  of  blood.  The  oxalate  solution  of  the  requisite 
amount  should  be  placed  in  a  vessel  and  the  blood  be  allowed  to  flow 
into  and  mix  with  it.  The  mixing  should  be  made  thorough  by 
vigorous  shaking.  To  produce  a  clot,  add  a  few  drops  of  a  2  per  cent 
solution  of  calcium  chloride  to  some  of  the  oxalate-blood.  The  potas- 
sium oxalate  prevents  clotting  by  precipitating  the  calcium  salts  nec- 
essary to  coagulation.  The  addition  of  calcium  chloride  restores  the 
calcium  and  renders  clotting  possible. 

74.  The  Minute  Structure  of  the  Fibrin  Framework.  —  To  a  drop  of 
fresh  blood  on  a  slide  add  two  drops  of  normal  salt  solution.  Put  on  a 
cover  glass  and  set  aside  an  hour  or  so  to  clot.  Add  50  per  cent  alco- 
hol at  the  edge  of  the  cover  glass  (to  wash  out  the  corpuscles  and 
harden  the  fibrin).  Observe  with  the  microscope  the  network  of 
fibrin  fibrils.  Care  must  be  taken  not  to  move  the  cover  glass  during 
the  preparation  for  examination. 


CHAPTER   XII 


THE   CIRCULATORY   SYSTEM 


211.  The  apparatus  distributing  the  blood  throughout 
the  body  and  keeping  it  constantly  in  motion  is  composed 
of  the  hearty  the  great  central 
pump;  arteries^  tubes  to  carry 
blood  from  the  heart ;  veins^  which 
are  tubes  carrying  blood  to  the 
heart ;  and  capillaries^  a  network 
of  small  tubes  connecting  arteries 
and  veins.  These  constitute  the 
vascular  system  (Fig.  85,  p.  146). 
In  addition  to  them  and  forming 
a  part  of  the  complete  circulatory 
system  are  the  lymphatics  and  lac- 
teals^  sometimes  called  the  lymph 
vascular  system.  They  are  tubes 
having  walls  thinner  than  those  of 
the  blood  vessels,  running  from 
periphery  to  center,  conveying 
lymph  and  chyle. 

212.  The  Heart  is  a  hollow,  cone- 
shaped  muscle,  inclosed  in  a  mem- 
branous sac  called  the  pericardium., 
lying  in  the  thorax  between  the  right  and  left  lungs  (Fig. 
86).     Its  base  is  directed  backward  and  upward,  while  its 

153 


Fig.  86.  —Front  view  of  the 
viscera  in  their  natural 
relations. 

The  heart  is  partly  covered 
by  the  lungs,  hut  its  true  out- 
line is  shown  by  a  dotted  line. 


154 


UNCONSCIOUS   NERVOUS   OPERATIONS 


apex  points  downward  and  forward  a  little  to  the  l-eft  of 
the  sternum,  or  breastbone.  The  heart  is  divided  longitu- 
dinally into  two  divisions  wholly  separate  from  each  other. 
Each  of  these  is  divided  again  into  two  chambers  which 
have   free   communication.       The    chambers  at   the   base 


Left  Pulmonary 
Artery 


Auricle 


Fig.  87.— Front  view  of  heart. 
Coronary  arteries  aucl  veins  are  injected,  arteries  red,  veins  blue. 


of  the  cone  are  called  the  right  and  left  auricles^  while 
the  other  two  are  called  right  and  left  ventricles  (Figs.  87 
and  88).  Lying  upon  the  outside  of  the  auricles  are  two 
flat  earlike  structures  which  are  called  the  right  and  left 
appendices. 

213.  The  Right  Auricle  lies  on  the  right  side  of  the  upper 
part  of  the  heart.  Its  walls  are  thin,  and  are  pierced  by 
openings  for  the  two  great  veins,  —  the  superior  veyia  cava^ 


THE   CIliCULATORY   SYSTEM 


155 


entering  from  above,  and  the  inferior  vena  cava^  entering 
from  below.  Tliese  two  veins  bring  to  the  heart  the  blood 
from  all  parts  of  the  body,  except  from  the  lungs  and  the 
.heart  itself.  Close  beside  the  inferior  vena  cava  the  coro- 
nary vein  opens  into  the  right  auricle.     This  brings  to 


Rifjht  Pulmonary  Artery 


Left  Pulmonary 
Artery^-~^^ 


Left  Pulmonary 
Vein:"^ 


Left  Auricle 


HJfjht  Pulmonary 


\laferior  Vena  Cava 


Fig.  88. —Heart  seen  from  behind. 

Coronary  arteries  and  veins  are  injected,  arteries  red,  veins  blue. 

the  auricle  the  blood  from  the  capillaries  of  the  heart 
itself,  which  like  all  other  organs  of  the  body  is  supplied 
with  blood  vessels  and  lymphatics  for  its  own  nutrition. 

214.  The  Left  Auricle  lies  at  the  left  and  back  of  the 
upper  part  of  the  heart.  Its  walls  are  slightly  thicker 
than  those  of  the  right  auricle.  It  receives  four  jj>w?77io- 
nary  veins,  two  from  each  lung.  The  openings  have  no 
valves. 


156 


UNCONSCIOUS  NERVOUS   OPERATIONS 


215.  The  Right  Ventricle  occupies  the  principal  part  of 
the  forward  surface  of  the  heart,  but  is  not  a  part  of  the 
apex.  The  walls  are  thicker  than  those  of  the  auricles 
and  less  smooth.  From  the  upper  side  of  the  cavity  of 
the  ventricle  a  large  opening  leads  to  the  great  pulmonary 
artery^  while  a  still  larger  opening  admits  the  blood  from 


Might  Auriculo-Ventricular 
Aperture  \ 


Xeft  Auriculo-Ventricular 
\  Aperture 


Aorta 

Pulmonary 
Artery 

:j^Semilunar  Valves 

i-i^.Flaps  of  Tricuspid 
Valve 


Papillary 
Muscles 


89. 


Right  ventricle,  cut  open  to  show  the  structures  that 
regulate  the  action  of  the  tricuspid  valve. 


the  right  auricle  (Fig.  89).  The  tricuspid  valves  prevent 
the  return  of  blood  from  the  ventricle  to  the  auricle.  The 
three  main  divisions  of  the  valve  and  three  smaller  ones 
are  all  triangular  in  shape,  and  are  attached  by  their  bases 
to  a  tendinous  ring  surrounding  the  opening.  The  thin- 
ner edges  of  the  valves  are  flajDS  of  transparent  membrane 


THE   CIRCULATORY   SYSTEM  157 

hanging  downward  and  held  by  slender  white  tendinous 
cords  attached  to  little  projecting  columns  in  the  walls  of 
the  ventricle  (^papillary  muscles^.  These  cords  and  mus- 
cles keep  the  valves  from  being  pressed  back  into  the 
auricle  further  than  is  necessary  to  close  the  communica- 
tion. Blood  can  thus  flow  from  the  auricle  into  the  ven- 
tricle, but  not  from  the  ventricle  to  the  auricle.  The 
passage  into  the  pulmonary  artery  is  guarded  by  three 
folds,  or  pockets,  in  the  lining  membrane,  called  semilunar 
valves^  which  have  their  free  edges  turned  upward,  so  that 
when  the  blood  is  forced  upward  into  the  artery,  the  valves 
lie  fiat  against  its  walls,  while  if  the  blood  should  begin  to 
flow  backward,  the  little  pockets  would  at  once  be  filled, 
their  edges  crowded  together  in  the  center  of  the  tube, 
and  the  opening  closed. 

216.  The  Left  Ventricle  occupies  the  chief  part  of  the 
hinder  surface  of  the  heart,  and  includes  the  apex  (Figs. 
87  and  88).  It  opens  at  its  upper  side  from  the  left  auricle 
and  into  the  aorta ^  t\\Q  great  artery  whose  branches  bear 
the  blood  to  the  general  system.  The  walls  are  much 
thicker  than  in  any  other  part  of  the  heart  because  greater 
force  is  required  here  to  send  the  blood  to  the  most  dis- 
tant parts  of  the  body. 

The  mitral  or  bicuspid  valves  guard  the  opening  into 
the  left  auricle.  They  are  similar  to  the  tricuspids, 
except  that  they  have  only  two  main  divisions  instead  of 
three.  Tendinous  cords  and  papillary  muscles  hold  their 
edges  in  place  as  in  the  case  of  the  tricuspids.  A  strong 
fibrous  ring  surrounds  the  end  of  the  aorta^  and  within  its 
mouth  are  three  semilunar  valves^  thicker  and  stronger 
than  those  of  the  pulmonary  artery.  Their  action  is  like 
that  of  the  other  semilunar  valves. 

217.  All   the    cavities    of   the    heart    are   lined  with  a 


158  UNCONSCIOUS   NERVOUS   OPERATIONS 

smooth,  shining  membrane,  the  endocardium^  which  also 
covers  the  valves,  and  is  continuous  with  the  lining  of  the 
veins  and  arteries. 

218.  Cardiac  Muscle.  —  As  stated  in  the  chapter  on  Mus- 
cles, the  muscular  fibers  of  the  heart  form  a  class  by  them- 
selves,   being   striped   but   involuntary    (Fig.    90).       The 

fibers  lie  side  by  side,  but  send  off  at  short 
intervals  branches  which  unite  them.  The 
muscular  fibers,  moreover,  are  arranged  in 
the  wall  of  the  heart  in  bundles  in  such  a 
way  that  in  contracting  they  draw  the  two 
sides  of  the  walls  of  the  chambers  together 
until  they  meet.  The  muscle  fibers  of  the 
walls  of  the  auricles  are  distinct  from  those 
90  — T  ^^  *^®  ventricles,  so  that  they  contract  sepa- 
cardiacmus-  rately,  as  we  shall  see.  Each  fiber,  or  muscle 
cle  fibers.  ^^^l^  contains  one  nucleus.  , 

Cardiac  muscle  fiber  appears,  to  a  large  extent,  to  origi- 
nate its  own  contraction,  and  is  not  so  entirely  as  is  a  skel- 
etal muscle  fiber  a  mere  instrument  of  a  motor  nerve 
fiber.  The  action  of  cardiac  muscle  under  stimulus  is  not 
stronger  or  weaker  in  proportion  to  the  strength  of  the 
stimulus,  as  is  the  case  with  skeletal  muscles.  A  weak 
electric  shock,  if  it  causes  any  beat  at  all  in  the  heart 
muscles,  causes  as  strong  a  beat  as  does  a  strong  stimulus. 

219.  Arteries  are  the  vessels  which  convey  the  blood 
from  the  ventricles  of  the  heart.  The  smallest  of  them 
have  a  few  plain  muscular  fibers  wrapped  round  the  tube 
outside  the  endothelium.  As  the  arteries  grow  larger, 
the  number  of  muscle  fibers  increases  till  they  form  a 
definite  muscular  coat  with  a  little  connective  tissue.  In 
the  lars^est  arteries  the  Avails  consist  of  three  layers  (Fig. 
91) :    (a)  the  inner  coat,  consisting  of  endothelium  with  a 


THE   CIRCULATORY   SYSTEM 


159 


thin  elastic  layer  on  its  outer  side;  (h)  a  muscular  and 
elastic  coat;  (c)  a  connective  tissue  coat,  forming  the 
outside  of  the  vessel.  The 
very  largest  arteries  have 
more  of  the  elastic  in  pro- 
portion to  the  muscular 
tissue.  Owing  to  the  pres- 
ence of  the  elastic  tissues, 
arteries  may  be  stretched 
leno'thwise,  or  distended 
by  pressure  from  -within, 
and  Avill  contract  when 
the  stretching  force  dis 
appears.  Arteries  have 
no  valves;  those  at  the 
beginning  of  the  aorta 
and  the  pulmonary  ar- 
tery belong  to  the  heart. 
Branches  of  the  smaller  arteries  often  run  into  one 
another,  so  that  there  is  more  than  one  path  for  the 
blood  from  point  to  point;  if,  by  any  means,  one  becomes 
closed,  the  blood  can  still  pass  round  by  another  way. 

220.  Veins  are  the  vessels  which  carry  the  blood  toward 
the  heart.  Great  arteries  open  from  the  ventricles.  The 
great  veins  open  into  the  auricles.  Their  walls  are 
thinner  than  those  of  the  arteries,  and  collapse  when  the 
veins  are  empty.  They  contain  less  of  the  elastic  and 
muscular  tissues  than  arteries.  Veins  are  supplied  with 
many  semilunar  valves,  which  prevent  the  blood  from 
flowing  in  the  wrong  direction. 

221.  Vascular  and  Nervous  Supply  of  Blood  Vessels. — The 
coats  of  arteries  and  veins  are  supplied  with  their  own 
arteries,    capillaries,  lymphatics,  and   veins    by  means  of 


Fig.  91.  — Cross  section  of  an  artery. 

a  smooth  inner  coat. 

b  middle  or  muscular  coat. 

c  outer  or  connective  tissue  coat. 

d  small  artery  to  nourish  the  large  one. 


160  UNCONSCIOUS   NERVOUS   OPERATIONS 

which  they  are  nourished;  and  nerve  fibers  from  sympa- 
thetic nerves  form  plexuses  around  the  blood  vessels  — 
plexuses  from  which  nerve  fibers  penetrate  between  the 
muscle  fibers  of  the  muscular  coat. 

222.  The  Capillaries  are  the  minute  branches  of  veins 
and  arteries  which  form  a  connection  and  means  of  com- 
munication between  the  two  sets  of  vessels.  Their  walls 
are  formed  of  an  extremely  thin  membrane  which  is  easily 
ruptured  by  unusual  pressure.  It  is  in  the  capillaries 
that  occur  all  the  changes  which  take  place  in  the  blood. 
In  the  web  of  a  frog's  foot,  under  the  microscope,  the 
movement    of  the  blood   in  the  capillaries  may  be  seen. 

223.  Osmosis  is  the  term  applied  to  the  phenomena  of 
interchange  between  different  fluids  when  in  contact  or 
when  separated  by  membranes  or  walls  having  minute 
23ores.  By  osmosis  the  blood  inside  the  capillaries  and  the 
tissue  elements  on  the  outside  become  intermingled,  and 
by  the  same  means  animal  tissues  live  upon  the  lymph, 
which  is  in  turn  replenished  by  the  blood,  while  certain 
elements  pass  from  the  protoplasmic  cells  of  the  tissues, 
by  means  of  the  lymph,  into  the  blood.  It  is  not  true, 
however,  that  osmosis  in  living  tissues  is  subject  to  the 
same  laws  as  that  which  takes  place  through  dead  animal 
or  vegetable  membranes. 

224.  Course  of  the  Blood  in  the  Body.  —  In  describing  the 
circulation  of  the  blood  it  is  customary  to  speak  of  the 
general  or  systemic  circulation^  the  pulmonary  circulation^ 
and  the  portal  circulation.  These  are  convenient  terms, 
and  are  here  retained  for  that  reason.  There  is,  however, 
but  one  circulation,  by  which  the  blood  leaving  any  one 
part  of  the  circulatory  system  returns  to  the  same  part 
again.  To  do  so  it  must  pass  through  two  sets  of 
capillaries  and  must  be  twice  returned  to  the  heart.     The 


THE    CIRCULATORY    SYSTEM 


161 


blood  of  the  portal  circulation  passes  in  the  liver  through 
a  third  set  of  capillaries. 


Fig.  92.  — Diagram  of  the  course  of  the  blood  in  the  circulation. 


225.  The  General  or  Systemic  Circulation  (Figs.  85  and 
92).  —  The  blood  leaves  the  heart  by  the  aorta^  which 
arises  from  the  left  ventricle   and  after  forming  a  large 


162 


UNCONSCIOUS   NERVOUS   OPERATIONS 


Siibclavian  Arteries^^ 


arch  over  the  root  of  the  left  lung  passes  downward  near 
the  spinal  column.  Piercing  the  diaphragm,  the  aorta 
enters  the  abdomen,  and  at  the  fourth  lumbar  vertebra 
divides  into  the  right  and  left  coynmon  iliac  arteries^  and  a 
third  small  branch  (the  middle  sacral)  which  continues  on 
to  the  end  of  the  coccyx. 

226.  Branches  of  the  Aorta  (Figs.  85  and  93).  —  The 
first  branches  of  the  aorta  are  the  two  coronary  arteries 
sent  off  just  beyond  the  semilunar  valves  to  supply  the 

Avails  of  the  heart.  The  large 
branches  from  near  the  top 
of  the  arch  are:  (1)  the  in- 
nominate  artery,  which  soon 
divides  into  two,  the  right  sub- 
clavian^ running  to  the  right 
arm,  and  the  7^ight  carotid,  sup- 
plying the  right  sid^  of  the 
head  and  neck;  (2)  the  left 
common  carotid  for  the  left  side 
of  the  neck  and  head;  and 
(3)  the  left  subclavian  artery 
for  the  left  arm.  Each  sub- 
clavian artery  gives  off  at  the 
armpit  the  axillary  and  in  the 
arm  the  brachial  artery.  The 
latter  divides  into  the  ulnar 
and  the  radial  arteries,  named 
from  the  bones  along  which  they  lie.  They  unite  in  the 
hand  to  form  the  palmar  arch. 

The  carotid  arteries  ascend  the  sides  of  the  neck  and 
divide  into  two  branches,  which  supply  the  head  and  face 
and  the  brain. 

The  branches  of  the  aorta  within  the  thorax  are  (besides 


Semilunar  Valves 


Fig.  93.  — Arch  of  the  aorta,  dis- 
sected free  from  the  rest  of 
the  heart. 


THE   CIRCULATORY   SYSTEM 


163 


the  coronary)  the  two  bronchial^  which  go  to  the  lungs; 
the  three  or  four  esophageal,  ior  tlie  coats  of  the  esopha- 
gus; the  pericardial,  for  the  pericardium;  and  numerous 
intercostal  arteries. 

Within  the  abdomen  arise  the  phrenic,  in  the  dia- 
phragm ;  the  coeliac  axis,  with  three  branches,  —  the 
hepatic,  going  mainly  to  the  liver,  the  gastric,  to  the  stom- 
ach, and  the  splenic  to  the  spleen  (Fig.  94)  ;  the  superior 


R.  Phrenic  Artery 
/'^Abdominal 
/    Aorta 

Ccp.Uac  Axis 
^  y  Gastric  Artery 
''/Splenic  Artery 


Hepatic  Artery 

Fig.  94.  — The  coeliac  axis  and  its  branches. 


and  inferior  mesenteric,  which  supply  the  intestine ;  and 
the  renal,  going  to  the  kidneys. 

The  iliac  arteries  supply  the  walls  and  organs  of  the 
pelvis  and  the  legs.  The  artery  on  the  front  and  inner 
side  of  the  thigh  is  called  the  femoral ;  above  the  knee 
joint  it  passes  to  the  back  side  of  the  leg,  and  is  there 
called  the  popliteal,  while  below  the  knee  the  main 
branches  are  the  tibial  and  the  peroneal^  which  unite  in 


164  UNCONSCIOUS  NERVOUS   OPERATIONS 

the  foot  in  a  palmar  arch.      All  these  arteries  give  off 
numerous  other  branches  all  along  their  course. 

227.  The  Principal  Veins  (Fig.  85).  —  The  blood  con- 
veyed by  the  arteries  to  the  capillaries  of  all  parts  of  the 
body  passes  there  into  the  small  veins,  which  unite  into 
larger  ones,  and,  in  general,  run  beside  the  arteries,  and 
often  have  corresponding  names.  They  are  gathered  into 
the  superior  vena  cava^  which  collects  the  blood  from  the 
head,  arms,  and  portions  of  the  chest ;  the  inferior  vena 
cava.,  by  which  the  blood  is  returned  from  the  remainder 
of  the  body  (the  lungs  and  heart  excepted)  to  the  heart ; 
and  the  coronary  vein  from  the  walls  of  the  heart.  All 
these  veins  empty  their  contents  into  the  right  auricle. 
Many  of  the  veins  are  provided  with  valves  to  prevent 
the  reflow  of  the  blood. 

228.  The  Pulmonary  Circulation  (Fig.  92).  —  From  the 
right  auricle  the  blood  flows  into  the  right  ventricte,  and 
by  its  contraction  is  forced  into  the  pulmonary  artery^ 
which,  dividing  into  two,  one  for  each  lung,  carries  the 
blood  to  the  capillaries  of  the  lungs.  It  is  then  collected 
by  the  pulmonary  veins  (two  from  each  lung)  and  returned 
to  the  left  auricle,  and  passes  thence  to  the  left  ventriclis, 
having  completed  the  circuit  of  the  body. 

In  the  systemic  circulation  the  arteries  convey  the  pure, 
oxidized,  nutrient  blood  to  the  capillaries,  while  the  veins 
return  the  impure,  deoxidized  blood  to  the  heart.  In  the 
pulmonary  circulation  the  reverse  is  true.  Impure  blood 
flows  through  the  pulmonary  arteries  to  be  oxidized  in 
the  lungs,  and  returned  pure  by  the  pulmonary  veins. 

229.  The  Portal  Circulation  is  an  accessory  and  peculiar 
circulation  belonging  to  the  liver.  That  organ  not  only 
receives  arterial  blood  through  the  hepatic  artery.,  but  is 
also  supplied   by  the  portal  vein  with  blood  which  has 


THE    CIRCULATORY    SYSTEM 


165 


already  circulated  through  the  capillaries  of  the  stomach, 
spleen,  intestines,  and  pancreas  (Fig.  95).  Unlike  any 
other  A'ein,  the  portal  vein  ends  in  a  second  set  of  capil- 


Gall  Bladder. 


Inferior 
'Mesenteric  Vein 


Inferior 
'Mesenteric  Artery 


Descending  Colon 


Small  Intestine 


Fig.  95.— The  portal  vein  and  its  chief  branches. 

The  liver  is  turned  back  and  the  transverse  colon  and  a  part  of  the  small 
intestine  are  cut  away. 


laries  around  the  cells  of  the  liver,  from  which  it  is  col- 
lected into  the  hepatic  veiiis^  which  open  into  the  inferior 
vena  cava. 


166 


UNCONSCIOUS   NERVOUS   OPERATIONS 


230.    ActioD  of  the  Heart  in  the  Circulation  (Fig.  96).  —  In 
the  heating  of  the  heart,  the  contraction  of  the  muscular 

walls  commences  at  the' 

A 

mouths  of  the  great 
veins  in  the  auricles, 
runs  through  the  two 
auricles  and  then  over 
the  two  ventricles  to- 
gether, the  auricles  be- 
ginning to  dilate  as  the 
ventricles  begin  to  con- 
tract. Then  there  is 
an  instant's  pause,  when 
neither  set  of  muscles 
are  contracting,  but  the 
whole  heart  is  expand- 
ing, and  its  waHs  are 
soft  and  flabby. 

The  impulse  from  the 
heart's  contraction  is 
felt  in  the  arteries  of 
the  wrist,  the  temples, 
and  some  other  parts  of 
the  body,  and  is  called 
the  pulse. 

During  the  pause  the 

relaxed    walls     of     the 

heart  yield  to  the  blood 

which    flows    into    the 

auricles   from   the   pul- 

Fig.  96.  —  Diagrams  illustrating  the  ac-     monary   veins    and    the 
tions  of  the  valves  of  the  heart.  rT^1 

vense  cavse.      ine  semi- 

A  during  the  filling  of  the  right  ventricle.  x      xi^ 

B  during  the  contraction  of  the  ventricle.        lunar       valvCS       at      the 


THE   CIRCULATORY   SYSTEM  167 

mouths  of  the  great  arteries  are  closed;  the  tricuspid  and 
mitral  valves  are  open.  The  ventricles  now  begin  to  dilate, 
and  the  blood  flows  freely  into  them  from  the  auricles. 
As  they  fill,  currents  in  the  blood  along  the  walls  carry  up 
the  flaps  of  the  valves  till  they  are  nearly  closed.  The 
auricles  now  contract,  the  contraction  beginning  at  the 
mouths  of  the  great  veins,  which  narrows  the  openings, 
and  more  blood  is  sent  into  the  ventricles.  This  swifter 
flow  into  the  ventricles  sets  up  stronger  back  currents 
along  their  walls,  and,  the  muscular  walls  beginning  to 
contract,  the  valves  are  completely  closed.  The  blood 
then  has  no  escape  but  by  the  arteries  issuing  from  the 
ventricles.  The  strong  walls  of  the  ventricles  press  more 
and  more  upon  the  imprisoned  blood,  it  is  forced  swiftly 
through  the  mouths  of  the  arteries,  pressing  back  the 
semilunar  valves,  and  the  ventricles  themselves  are  empty 
before  they  begin  to  relax  again.  When  relaxation  sets 
in,  the  return  of  arterial  blood  into  the  ventricles  is  pre- 
vented by  the  semilunar  valves. 

231.  Sounds  of  the  Heart.  — Two  distinct  sounds  from  the 
heart  may  be  detected  by  placing  the  ear  over  the  region 
of  that  organ.  The  first  is  dull  and  somewhat  prolonged, 
the  second  is  shorter  and  sharper.  The  first  may  be  heard 
immediately  before  the  pulse  is  felt  at  the  wrist,  the  sec- 
ond immediately  after  it.  They  are  followed  by  a  brief 
silence.  The  exact  cause  of  the  first  sound  in  not  fully 
determined,  but  it  is  thought  that  it  may  be  partly  due  to 
vibrations  of  the  tendinous  cords  attached  to  the  heart 
valves  themselves,  and  partly  to  a  muscular  sound  pro- 
duced by  contraction  in  the  mass  of  muscular  fibers  in 
the  ventricles.  The  second  sound  occurs  at  the  moment 
of  closure  of  the  semilunar  valves,  and  is  due  to  the  strik- 
ing together  of  those  valves. 


168  UNCONSCIOUS  NERVOUS   OPERATIONS 

232.  Action  of  the  Arteries.  —  All  the  blood  vessels  are 
always  full  of  blood,  —  at  the  moment  of  the  heart's  pause, 
as  at  every  other.  When,  therefore,  the  contraction  of 
the  left  ventricle  forces  from  four  to  six  additional  ounces 
of  blood  into  the  aorta,  that  which  already  fills  the  vessels 
must  be  crowded  on.  In  the  minute  tubes  of  the  capil- 
laries there  is,  however,  a  very  considerable  amount  of 
friction  to  be  overcome,  and  as  beat  follows  beat,  the 
elastic  walls  of  the  arteries  must  stretch  to  receive  the 
flow.  The  elastic  arteries  also  react  upon  the  blood 
between  the  beats  to  force  it  through  the  capillaries. 
Thus  the  flow,  which  is  intermittent  in  the  arteries, 
becomes  continuous  in  the  capillaries. 

The  muscular  contraction  in  the  arteries  helps  to  regu- 
late the  amount  of  blood  sent  to  different  parts  at  different 
times.  Many  familiar  facts  illustrate  this.  Blushing  is 
due  to  an  increased  flow  of  blood  to  the  face ;  a  mustard 
plaster  draws  more  blood  to  the  area  which  it  covers  ; 
friction  of  the  surface  has  a  like  effect.  After  death  the 
arteries  are  always  found  empty,  their  last  contraction 
having  forced  the  blood  into  the  veins. 

233.  Blood  Pressure.  —  During  life  the  elastic  walls  of 
the  arteries  are  always  distended,  and  the  pressure  upon 
their  walls  of  the  extra  quantity  of  blood  forced  into 
them  by  the  beating  of  the  heart  is  called  blood  pres- 
sure. When  an  artery  is  cut,  it  is  noticed  that  the  blood 
issues  from  it  in  jets  corresponding  to  the  beats  of  the 
heart,  and  the  nearer  the  cut  is  to  the  heart,  the  stronger 
is  the  spurt.  When  a  vein  is  severed,  on  the  other  hand, 
the  flow  is  steady  and  with  less  force. 

The  difference  in  the  amount  of  blood  pressure  in  veins 
and  arteries  is  shown  by  experiments  upon  animals.  If  a 
long  glass  tube  be  introduced  into  the  carotid  artery  of 


THE   CIRCULATORY   SYSTEM  169 

a  rabbit,  for  instance,  the  blood  will  rise  in  the  tube  to  a 
height  of  about  three  feet,  and  will  be  raised  slightly 
farther  at  each  beat  of  the  heart.  If  a  similar  tube  be 
placed  in  an  opening  in  the  jugular  vein,  the  blood  will 
rise  in  the  tube  only  very  slightly,  and  the  height  will 
not  be  affected  by  the  heart  beats. 

234.  Velocity  of  the  Blood.  —  Of  course  the  same  quan- 
tity of  blood  flows  through  the  aorta  as  flows  through  all 
the  capillaries  of  the  system  and  is  returned  to  the  right 
auricle  ;  but  all  the  capillaries  together  hold  much  more 
blood  than  the  aorta.  The  blood  must,  therefore,  pass 
more  rapidly  through  the  aorta  than  through  the  capil- 
laries. Its  rate  is  about  fifteen  inches  a  second  in  the 
aorta,  and  about  half  that  in  the  two  venae  cavce,  while 
in  the  capillaries  it  is  thought  to  be  less  than  one  twenti- 
eth of  an  inch  in  a  second. 

235.  The  Lymphatic  Circulation.  — We  have  seen  (§  209) 
that  the  plasma  of  the  blood  which  oozes  through  the  thin 
walls  of  the  blood  capillaries  forms  the  fluid  called  lymph. 
This  fluid  contains  corpuscles  apparently  identical  with  the 
white  blood  corpuscles,  but  no  red  ones.  As  it  fills  the 
spaces  between  the  cells  of  the  tissues  it  conveys  nutri- 
ment directly  to  the  cells  themselves  in  all  parts  of  the 
body.  A  network  of  delicate  vessels  called  lymph  capil- 
laries carries  away  the  surplus  fluid.  The  walls  of  these 
tubes  are  extremely  thin,  being  composed,  like  the  blood 
capillaries,  of  a  single  layer  of  flat  cells  with  a  little  con- 
nective tissue  and  a  few  plain  muscular  fibers.  The  small 
vessels  unite  to  make  up  larger  ones,  which  are  supplied 
with  valves,  like  the  veins,  and  all  finally  pour  their  con- 
tents into  two  large  tubes.  One  of  these  is  called  the 
thoracic  duct,  and  runs  upward  in  the  thorax  and  abdomen 
along  the  spinal  column  to  empty  into  the  angle  of  June- 


170 


UNCONSCIOUS   NERVOUS   OPERATIONS 


Right 
LymphatiA 


Fig.  97. 


The  thoracic  duct  and  right 
lymphatic  duct. 


tion  of  the  large  jugular 
vein  in  the  neck  with  the 
left  subclavian  (Fig.  97). 
The  other  is  the  right 
lymphatic  duct^  and  opens 
into  the  angle  of  junc- 
tion of  the  right  internal 
jugular  and  subclavian 
veins.  The  thoracic  duct 
receives  on  its  way  the 
contents  of  the  lacteals, 
and  the  whole  is  poured 
into  the  blood  stream. 
Lymph  is  an  alkaline 
fluid,  and  contains  a 
larger  proportion  of  the 
Avaste  products  of  the 
vital  processes  than  does 
the  blood. 

Nervous  connection  be- 
tween the  muscular  fibers 
of  the  lymphatic  vessels 
and  the  nerve  centers  has 
not  been  traced,  though 
from  what  is  known  of 
nervous  control  over  oth- 
er organs  and  processes 
in  the  body,  it  is  believed 
to  exist. 

236.  Lymphatic  Glands. 
—  Throughout  the  lym- 
phatic system  colorless 
or    white   corpuscles  are 


THE   CIRCULATORY   SYSTEM  171 

found.  Some  of  these  pass  through  the  walls  of  the  blood 
capillaries  with  the  plasma  which  forms  the  lymph,  but 
all  along  the  course  of  the  lymphatics  are  small  glands 
made  of  networks  of  connective  tissue  which  hold  in  their 
meshes  large  numbers  of  small  Avhite  corpuscles  packed 
side  by  side  as  closely  as  possible.  The  lymph,  flowing 
into  these  glands  on  one  side  and  from  them  on  the  other 
side,  carries  along  with  it  some  of  these  corpuscles  and 
thus  keeps  the  blood  supplied.  These  lymphatic  glands, 
or  similar  tissues  in  the  body,  are  the  source  of  the  white 
corpuscles  of  the  blood. 

237.  Hygiene  of  the  Circulation.  —  In  perfect  health  the 
blood  cir'culates  rapidly,  because  the  heart  beats  strongly, 
the  muscular  tone  of  arteries  and  veins  is  such  as  to  pro- 
mote the  flow,  the  blood  is  purified  in  the  lungs  by  an 
abundant  supply  of  pure  air,  plenty  of  fresh  material  is 
supplied  to  it  from  suitable,  well-digested  food,  the  nerv- 
ous centers  are  quickly  responsive  to  their  natural  stimuli, 
and  furnish  the  needful  impulse  to  the  numerous  parts  of 
the  circulatory  apparatus. 

The  blood  cannot  circulate  freely  unless  the  whole  body 
is  so  loosely  clothed  that  there  is  no  pressure  upon  any  of 
the  blood  vessels,  no  restriction  of  the  breathing  capacity, 
no  interference  with  the  normal  action  of  the  stomach, 
liver,  and  intestines.  There  must  be  exercise  of  all  the 
muscles,  sleep  sufficient  to  keep  the  nervous  system  in 
good  condition,  and  activity  of  the  excretory  organs. 
The  last  is  promoted  by  exercise,  frequent  bathing, 
friction  of  the  skin,  and  the  wearino-  of  woolen  under- 
garments. 

238.  Effects  of  Alcohol  upon  the  Blood  and  the  Circulation.  — 
The  first  effect  of  dilute  alcohol  taken  into  the  stomach 
appears   to   be   to  make   the  heart  beat   faster  and  with 


172  UNCONSCIOUS  NERVOUS   OPERATIONS 

more  force,  to  expand  the  smaller  blood  vessels  of  the 
skill,  and  to  cause  a  more  rapid  flow  of  blood  to  the  sur- 
face. This  produces  a  comfortable  glow  in  the  skin,  and 
the  drinker  thinks  he  has  been  warmed  by  his  glass  of  wine 
or  beer  or  weak  spirits.  As  a  matter  of  fact,  however, 
most  of  the  additional  heat  brought  to  the  surface  by  the 
increased  flow  of  warm  blood  very  soon  passes  off  and  is 
followed  by  chilliness  ;  for  the  general  bodily  tempera- 
ture, though  at  first  raised  by  the  oxidation  of  the  alcohol, 
is  finally  lowered  by  the  increased  radiation  from  the 
surface. 

Alcohol  in  the  stomach  is  rapidly  absorbed  and  passes 
into  the  blood  stream.  There  the  strong  affinity  of  alco- 
hol for  oxygen,  which  leads  them  to  enter  very  rapidly 
into  chemical  combination,  causes  the  alcohol  to  appropri- 
ate the  oxygen  of  the  red  corpuscles  of  the  blood,  which, 
as  we  have  seen  (§  205),  are  the  great  oxygen  carriers 'in 
the  body.  This  tends  to  impoverish  the  blood  and  render 
it  less  valuable  to  the  tissues. 

The  immediate  stimulation  to  the  heart's  action  soon 
passes  away  and,  like  other  muscles,  the  muscles  of  the 
heart  lose  power  and  contract  with  less  force  after  having 
been  excited  by  alcohol. 

239.  Effects  of  Tobacco  upon  the  Circulation.  —  The  fre- 
quent use  of  cigars  or  cigarettes  by  the  young  seriously 
affects  the  quality  of  the  blood.  The  red  blood  corpus- 
cles are  not  fully  developed  and  charged  with  their  nor- 
mal supply  of  life-giving  oxygen.  This  causes  paleness 
of  the  skin,  often  noticed  in  the  face  of  the  young  smoker. 
Palpitation  of  the  heart  is  also  a  common  result,  followed 
by  permanent  weakness,  so  that  the  whole  system  is 
enfeebled,  and  mental  vigor  is  impaired  as  well  as  physical 
strength.     Observant  teachers  can  usually  tell  which  of 


THE   CIRCULATORY   SYSTEM  173 

the  boys  under  their  care  are  addicted  to  smoking,  simply 
by  the  comparative  inferiority  of  their  appearance,  and 
by  their  intellectual  and  bodily  indolence  and  feebleness. 
After  full  maturity  is  attained  the  evil  effects  of  com- 
mencing the  use  of  tobacco  are  less  apparent  ;  but  com- 
petent physicians  assert  that  it  cannot  be  safely  used  by 
those  under  the  age  of  forty. 


Demonstrations  and  Experiments 

75.  Dissection  of  the  Heart.  —  Order  of  a  butcher  the  heart  of  a  calf, 
sheep,  or  pig.  Explicit  directions  should  be  given  that  the  entire 
"pluck"  be  saved,  i.e.  heart,  lungs,  and  larger  blood  vessels  intact; 
otherwise  mutilated  specimens  will  be  received.  By  inflating  the 
lungs  through  the  trachea  their  structure  and  general  relationship 
to  the  heart  can  be  shown.  Observe  that  the  heart  lies  in  a  sac,  the 
pericardium.  Cut  open  the  latter  and  notice  the  pericardial  fluid. 
Before  proceeding  to  cut  open  the  heart  identify  as  many  as  possible 
of  its  parts  and  connected  blood  vessels.  Observe  the  blood  vessels 
connecting  the  heart  and  the  lungs,  and  distinguish  between  the 
pulmonary  artery  and  the  pulmonary  veins.  The  aorta  and  the  two 
vense  cavse  can  be  distinguished  with  very  little  trouble.  After  sever- 
ing the  vessels  connecting  the  heart  with  the  lungs,  the  course  of  the 
blood  through  the  heart  can  be  shown,  and  a  difference  between 
the  arteries  and  the  veins  can  be  demonstrated  by  forcing  water  into 
the  vessels.  Water  injected  through  the  venae  cavse  into  the  auricle 
emerges  from  the  pulmonary  artery.  Injected  in  the  opposite  direc- 
tion the  flow  is  retarded  by  the  auriculo-ventricular  valve.  In  this 
way  one  can  identify  vessels  of  which  he  is  in  doubt,  and  demonstrate 
the  functions  of  the  valves.  Demonstrate  the  internal  structure  of 
the  heart  by  making  incisions  in  the  walls  of  the  auricles  and  ventri- 
cles, and  identifying  the  parts  as  described  in  the  text. 

76.  Demonstration  of  the  Organs  of  Circulation.  — The  principal  ves- 
sels of  the  circulatory  system  can  be  readily  dissected  out  in  the  body 
of  a  cat,  dog,  or  rabbit.  If  the  teacher  is  familiar  with  methods  of 
injecting  the  circulatory  system  with  some  colored  substance,  the 
vessels  can  be  more  easily  traced  out,  and  also  preparations  can  be 

macy's  phys.  — 11 


174  UNCONSCIOUS  NERVOUS   OPERATIONS 

made  that  will  keep  permanently  in  suitable  preservative  fluids.  But 
the  larger  blood  vessels  can  be  easily  dissected  out  in  uninjected 
specimens. 

77.  Structure  of  Blood  Vessels.  —  Prepared  cross  sections  of  the  walls 
of  blood  vessels  can  be  purchased,  or  borrowed  from  some  local 
physician.  The  blood  vessel  is  seen  to  be  composed  of  three  coats : 
inner,  epithelial ;  middle,  largely  muscular ;  and  outer,  fibrous. 

78.  Circulation  in  the  Web  of  the  Frog's  Foot.  —  The  frog  should  be 
placed  in  a  small  cloth  bag,  one  foot  being  allowed  to  protrude.  The 
animal  should  then  be  tied  upon  a  board  or  wooden  frame  with  the 
web  of  its  foot  stretched  over  an  opening  in  the  board.  The  web 
may  be  kept  stretched  by  the  aid  of  strings  tied  to  the  toes.  The 
apparatus  should  then  be  placed  so  that  the  web  over  the  hole  in  the 
frame  lies  directly  under  the  objective  of  a  compound  microscope.  If 
the  animal,  and  especially  the  web  of  the  foot,  be  kept  moist,  and  the 
cords  confining  it  are  not  too  tight,  the  movements  of  the  blood 
corpuscles  can  be  studied  for  a  long  time.  The  experiment  may  be 
performed  with  little  discomfort  to  the  frog. 

79.  Valves  in  Veins  can  be  shown  by  pressing  firmly  with  the  finger 
upon  one  of  the  veins  of  the  forearm,  and  then  passing  the  finger 
up  along  the  vein  toward  the  hand.  The  positions  of  the  valves  are 
indicated  by  the  temporary  swellings  that  make  their  appearance  as 
the  blood  is  forced  back  against  the  flaps  of  the  valves. 

80.  Scheme  of  the  Circulation.  —  The  general  features  of  the  circu- 
lation can  be  illustrated  with  the  apparatus  shown  in  Fig.  98.  The 
mechanism  can  be  easily  constructed,  requiring  only  some  rubber  and 
some  glass  tubing,  a  few  glass  Y-tubes,  some  pinchcocks,  and  a  bulb 
syringe. 

81.  To  illustrate  Arterial  and  Venous  Pressure  and  Flow.  —  Remove 
the  clamp  from  tube  C,  and  force  water  through  the  apparatus  with 
quick,  regular  strokes.  The  mercury  in  the  manometers  rises  and  falls 
with  each  stroke,  and  the  water  issues  in  jets  from  E.  Clamp  C.  and 
continue  as  before.  The  mercury  in  manometer  M  oscillates  c~>ut 
rises  higher  than  before,  with  a  marked  excess  of  rise  over  fall,  so 
that  finally  the  mercury  in  one  limb  of  the  manometer  stands  at  a 
considerable  height,  showing  vibrations  with  each  stroke  of  the  pump. 
In  manometer  N  the  mercury  rises  slowly,  with  little  or  no  oscillation, 
but  the  pressure  is  not  so  great  as  in  M.  The  water  issues  from  E 
in  a  steady  stream.     Open  clamp  at  D\  the  water  issues  in  iets  corre- 


THE   CIRCULATORY    SYSTEM 


175 


spending  to  the  strokes  of  the  pump.  While  working  the  pump  press 
lightly  with  the  finger  on  the  rubber  tubing  of  the  arterial  side  ;  a 
distinct  pulsation  is  felt  with  each  stroke.  Repeat  the  same  on  the 
venous  side. 

82.  Osmosis.  —  Prepare  a  dialyzer  by  tying  a  thin  animal  membrane 
(sausage  skins,  to  be  obtained  of  a  butcher,  furnish  excellent  mem- 
branes foi'  osmosis)  over  one  end  of  a  small  lamp  chimney.  Partly 
fill  the  dialyzer  with  a  strong  solution  of  sugar  and  place  it  in  a  larger 
vessel  of  pure  water,  so  that  the  liquids  in  the  two  vessels  are  at  the 
same  level.  In  a  short  time  the  contents  of  the  dialyzer  begin  to  rise, 
owing  to  the  greater  flow  toward  the  denser  liquid.  It  will  also  be 
found  that  the  water  in  the  outer  vessel  becomes  sweet  as  osmosis 
goes  on.  If  the  membrane  is  allowed  to  become  thoroughly  dry  after 
being  tied  on  the  dialyzer,  osmosis  goes  on  more  rapidly. 


M  N 


Fig.  98.  — Apparatus  for  illustrating  the  circulatory  system. 

bulb  syringe,  by  which  water  is  forced  through  the  apparatus. 

rubber  tubing  packed  with  bits  of  sponge  to  represent  capillaries. 

rubber  tube  connecting  arterial  and  venous  regions.   When  C  is  closed  with 

the  pinchcock  the  liquid  must  all  pass  tlirough  tubes  B. 
small  tube  ending  in  capillary  point  and  closed  with  a  pinchcock.     When 

open  it  allows  arterial  "  spurting  "  to  be  demonstrated, 
tube  which  shows  venous  flow.    It  ends  in  a  tube  of  small  caliber  in  order 

to  produce  a  venous  pressure. 
M,  N  manometers  consisting  of  glass  tubing  bent  in  a  U-shape  and  partly 

filled  with  mercury.    They  show  the  pressure  applied  to  the  arterial  and 

venous  sides  respectively. 


E 


CHAPTER  XIII 

NERVOUS  CONTROL  OF  THE  CIRCULATION 

240.  Functions  of  the  Nerves  of  the  Circulatory  System.  — 

When  any  special  activity  is  required  of  one  of  the  organs 
of  tlie  body,  an  increased  flow  of  blood  is  needful  to  that 
part.  There  is  not  blood  enough  in  the  body  to  enable 
all  the  muscles,  all  the  organs  of  digestion,  the  brain,  and 
the  organs  of  respiration,  etc.,  to  work  in  full  activity  at 
the  same  time.  There  must  therefore  be  some  method  of 
regulating  the  activities  of  the  different  parts  and  f)rgans, 
so  that  some  may  rest  while  others  work. 

Then,  too,  some  arrangement  must  exist  for  correlating 
the  action  of  the  heart  and  the  blood  vessels,  so  that  the 
steady  flow  of  nourishing  blood  may  be  kept  up  in  all  the 
capillaries,  with  more  powerful  pressure  applied  when  and 
where  it  is  needed,  and  not  at  the  wrong  place  and  the 
wrong  time. 

As  everywhere  else,  we  find  that  in  the  circulatory 
system  the  nerves  furnish  the  controlling,  coordinating, 
and  regulating  force. 

241.  Nerves  of  the  Heart  (Fig.  99). — Three  sources  of 
nervous  control  of  the  heart  are  usually  mentioned.  They 
are  the  cardiac  or  heay^t  branches  of  the  tenth  and  eleventh 
pairs  of  cranial  nerves,  —  the  vagus  or  pn eumog as f r ic  ^nd 
the  spinal  accessory;  the  cardiac  branches  of  the  sympa- 
thetic^ from   the  ganglia  of  the    neck;    and    what   have 

176 


NERVOUS   CONTROL   OF  THE   CIRCULATION 


177 


been  called  the  intrinsio  nerves  of  the  heart,  Avhich  were 
formerly  treated  as  uidependent  of  the  other  two  sets 
of  nerve  libers.  The  intrin- 
sic nerves  are  now  known, 
however,  to  be  merely  the 
terminations  of  the  other 
nerves  in  the  heart  wall, 
while  the  rhythmic  beat  of 
the  ventricles,  which  is 
fonnd  to  continue  for  some 
time  even  after  the  heart 
is  removed  from  the  body, 
is  believed  to  be  a  peculiar 
property  of  the  heart  muscle 
itself. 

242.  Path  of  the  Nervous 
Impulse.  — ■  The  roots  of  the 
vagus  and  the  spinal  acces- 
sory nerves  rise  near  together 
in  the  gray  matter  of  the 
medulla  oblongata.  A  branch 
from  the  spinal  accessory 
soon  joins  the  vagus,  and 
supplies  some  of  its  motor 
or  efferent  fibers.  Fibers 
from  the  sympathetic  nerves 
of  the  neck  also  join  the  va- 
o'us.  These  have  been  traced 
back  into  the  spinal  cord. 
The  cardiac  nerves,  there- 
fore, are  all  connected  with 
the  central  nervous  system, 
and,  since  all  parts    of   the 


Fig.  99.  — Diagram  illustrating  the 
nervous  control  of  the  heart. 


Sy 


cardiac  accelerator  center. 

accelerator  fibers  connected  with 
accelerator  center  through  sym- 
pathetic system  (Sij),  spinal 
nerves  (S) ,  and  spinal  cord. 

fibers  through  which  the  cerebrum 
exercises  control  over  the  car- 
diac centers. 

fibers  from  the  heart  that  excite 
the  inhibitory  center. 

cardiac  iuhibitory  center. 

inhibitory  fibers  whose  action 
slows  the  heart's  beating. 

communicating  fibers  between 
spinal  nerves  and  sj'mpathetic 
system. 

sympathetic  system. 


178  UNCONSCIOUS   NERVOUS   OPERATIONS 

spinal  cord  communicate  with  the  brain,  they  are  all  con- 
nected with  the  brain  also.  Certain  fibers  of  the  vagus 
j)roper  carry  the  afferent  influences  from  the  heart  to  the 
brain,  and  by  them  the  brain  is  kept  informed  of  the 
heart's  condition.  Fibers  of  the  spinal  accessory  and 
the  sympathetic  nerves  convey  motor  impulses  from  the 
brain  to  the  heart. 

243.  Accelerator  Fibers  of  Cardiac  Nerves.  —  Experiments 
have  proved  that  it  is  the  fibers  from  the  sympathetic 
ganglia  which  convey  to  the  heart  the  impulse  which 
accelerates  and  strengthens  its  beat.  They  are  supposed 
to  run  up  the  spinal  cord  to  an  accelerator  center  in  the 
medulla  oblongata  (Fig.  99). 

244.  Inhibitory  Fibers  of  Cardiac  Nerves.  — Stimulation  of 
the  fibers  of  the  motor  branch  of  the  vagus  running  to  the 
heart  not  only  does  not  increase  its  action,  but  retards  or 
inhibits  it,  and  may  entirely  stoj)  its  beating.  By  this 
means  the  brain  keeps  a  continual  check  upon  the  action 
of  the  heart.  It  has  been  found  that  if  the  vagus  nerves 
of  a  dog  are  divided,  the  beat  of  the  heart  is  quickened. 

245.  Reflex  Inhibition.  —  A  violent  blow  upon  the  stom- 
ach or  abdomen,  as  is  well  known,  may  cause  fainting,  due 
to  stoppage  of  the  heart's  action.  The  stimulus  of  the 
blow  is  carried  by  the  sympathetic  nerves  of  the  epigas- 
tric plexus,  situated  around  the  pit  of  the  stomach,  to  the 
thoracic  ganglia  and  thence  to  the  medulla  oblongata. 
There  the  impulse  is  reflected  along  the  efferent  fibers  of 
the  vagus  to  the  heart  muscles,  and  their  action  is 
checked.  Fainting  may  be  caused  in  a  similar  way  by 
the  action  of  severe  pain  or  strong  emotion  upon  the  nerve 
cells  of  the  brain.  The  impulse  reaches  the  region  of  the 
medulla  oblongata  from  which  the  vagus  arises,  and  is 
sent  on  to  the  heart. 


NERVOUS   CONTROL   OF   THE    CIRCULATION  179 

246.  Regulation  of  Blood  Pressure   in  the  Brain.  —  The 

regulation  of  blood  pressure  in  the  brain  is  by  means  of 
the  inhibitory  nerves.  Excitement  in  the  brain  increases 
blood  pressure  there,  and  that  pressure  gives  rise  to 
inhibitory  impulses  by  which  the  heart's  action  is  re- 
strained and  danger  to  the  brain  is  averted.  Or,  the 
inhibition  may  be  a  reflex  impulse  originating  in  the  heart 
itself  and  sent  up  to  the  inhibitory  center  by  the  afferent 
fibers  of  the  vagus,  and  tlie  heart  may  be  thus  enabled  to 
regulate  its  action  according  to  its  own  necessities. 

247.  The  Vasomotor  Nervous  System  is  tliat  which  regu- 
lates muscular  action  in  the  blood  vessels.  It  belongs  to 
the  sympathetic  system.  The  muscles  of  arteries  and 
veins  are  composed  of  plain  muscular  fibers,  and  the 
nerves  belonging  to  them  appear  to  end  in  fine  plexuses 
round  the  fibers.  Two  sets  of  nerves  for  the  blood  vessels 
have  been  made  out,  called  the  vasoconstrictor  and  the 
vasodilator^  whose  influences  correspond  to  the  influences 
of  the  accelerator  and  inhibitory  fibers  of  the  cardiac 
nerves.  It  should  be  noted  that  in  the  vertebrate  ani- 
mals no  inhibitory  nerve  fibers  exist  in  the  nerves  supply- 
ing the  voluntary  muscles,  while  the  involuntary  muscles 
usually  have  both  accelerator  and  inhibitory  fibers. 

248.  The  Vasoconstrictor  Nerves  have  been  traced  to  the 
ganglia  of  the  sympathetic  chain  and  thence  to  the  ante- 
rior horns  of  the  spinal  cord.  From  there  fibers  pass  up 
to  the  vasomotor  center  in  the  gray  matter  of  the  medulla 
oblongata. 

249.  Vasodilator  Nerves  accompany  the  vasoconstrictor 
for  a  part  of  their  course,  and  finally  reach  the  same  center 
in  the  medulla.  They  carry  inhibitory  impulses,  that  is, 
their  action  checks  the  contraction  of  the  muscle  fibers 
in  the  blood  vessels  and  permits  them  to  dilate. 


180  UNCONSCIOUS  NERVOUS   OPERATIONS 

250.  Effects  of  Vasomotor  Action.  —  The  muscular  action 
of  the  arteries  gives  its  general  tone  to  the  arterial  system 
and  regulates  the  flow  of  blood  in  the  whole  body,  and 
this  general  tone  is  influenced  by  the  central  nervous  sys- 
tem. For  instance,  certain  kinds  of  mental  excitement 
which  affect  the  brain  result  in  dilation  of  the  arteries  of 
the  face,  which  permits  a  more  ample  flow  of  blood  to  that 
part,  causing  what  is  called  blushing.  An  opposite  effect 
may  be  produced  by  emotion,  causing  pallor.  The  action 
is  mainly  reflex.  So  also  in  the  case  of  the  vessels  of  the 
skin.  When  the  temperature  is  low,  they  are  constricted 
and  the  surface  becomes  pale.  As  the  temperature  rises 
the  vessels  dilate  and  the  skin  becomes  flushed.  While 
these  changes  occur  upon  the  surface,  changes  of  a  reverse 
order  take  place  in  the  viscera,  and  the  temperature  of  the 
body  is  thus  largely  regulated.  Certain  poisons  in  the 
blood  circulating  through  the  brain  affect  the  vasomotor 
center,  as  when  the  blood  is  imperfectly  oxygenated  and 
therefore  impure,  resulting  sometimes  in  suffocation. 

251.  Alcoholic  beverages  affect  the  delicate  adjustment 
of  the  vasoconstrictor  and  vasodilator  nervous  forces 
and  may  seriously  interfere  with  the  circulation.  As  pre- 
viously stated,  dilute  alcohol  causes  the  constrictor  muscles 
in  the  capillaries  to  relax  so  that  the  capillaries  become 
dilated,  and  by  the  continued  use  of  alcoholic  drinks  they 
may  become  permanently  expanded. 


CHAPTER   XIV 

RESPIRATION 

252.  Definition.  —  The  lymph  obtains  from  the  blood  in 
the  capillaries  and  conveys  to  the  tissues  all  that  they 
need  for  sustaining  their  life.  Their  waste  products  are 
returned  to  the  blood.  One  important  element  which  all 
the  tissues  need,  is  oxygen,  and  one  important  element  in 
the  waste  is  carbon  dioxide,  or  carbonic  acid  gas. 

Respiration  is  the  process  by  which  oxygen  is  supplied 
to  the  blood  and  an  excess  of  carbonic  acid  is  removed  from 
it.  As  a  general  term,  respiration  includes  also  the  inter- 
change of  these  gases  in  the  tissues,  called  interyial  respi- 
ration^ or  tissue  respiration,  but  the  word  is  more  com- 
monly restricted  to  that  part  of  the  process  which  takes 
place  in  the  lungs. 

253.  The  Respiratory  Apparatus  consists  of  .the  channels 
through  which  air  passes  to  reach  the  capillaries  of  the 
lungs,  viz.  nostrils  and  mouthy  pharynx^  larynx^  trachea, 
bronchi^  bronchial  tubes,  alveoli^  and  air  cells ;  together 
with  the  muscles  of  the  chesty  of  the  diaphragm^  and  of 
the  abdomen. 

254.  Normally  the  air  enters  the  pharynx  through  the 
nostrils  rather  than  the  mouth.  By  passing  through  the 
winding  passages  of  the  nose  it  acquires  nearly  the  tem- 
perature of  the  body,  and  is  also  relieved  of  some  of  the 
particles  of  dust  always  floating  in  the  atmosphere. 

181 


182 


UNCONSCIOUS   NERVOUS   OPERATIONS 


255.  The  Trachea  is  a  large  tube  of  from  sixteen  to 
twenty  incomplete  cartilaginous  rings  (Fig.  100).  It  is 
from  four  to  four  and  a  half  inches  in  length,  from  the 


Fig.  100  —Diagram  of  the  respiratory  organs. 

cricoid  cartilage,  to  which  it  is  attached  above,  to  its 
lower  extremity,  where  it  divides  into  two  bronchi^  one 
of  which  goes  to  each  lung.  At  the  back  of  the  trachea, 
between  the  ends  of  the  cartilage  rings,  are  bands  of  plain 


RESPIRATION 


183 


muscular  fiber,  whose  function  is  to  draw  the  ends  of  the 
rings  together  and  reduce  the  caliber  of  the  tube.  The 
whole  tube  is  inclosed  in  a  fibrous  membrane,  and  lined, 
like  the  rest  of  the  passages,  with  mucous  membrane.  The 
superficial  layer  of  the  epithelium  of  the  trachea  is  ciliated^ 
that  is,  supplied  with  minute 
hairlike  prolongations. 

256.  The  Bronchi  resemble 
the  trachea  in  structure,  but 
have  a  distinct  layer  of  plain 
muscle  running  around  them. 

257.  The  Bronchial  Tubes 
and  Alveoli.  —  The  bronchi 
have  numerous  branches  called 
bronchial  tubes  reaching  to 
all  parts  of  the  lungs,  each 
branch  ending  finally  in  a 
wider,  funnel-shaped  passage, 
the  alveolus^  surrounded  by 
clusters  of  short,  somewhat 
dilated  sacs,  the  air  cells  (Fig.  101) .   All  the  tubes  are  lined, 

like  the  trachea,  with  ciliated  epithelium. 
The  cilia  being  continually  in  motion 
drive  out  the  mucus  which  is  constantly 
secreted,  and  along  with  it  the  dust 
brought  into  the  passages  with  the  air. 
258.  The  Air  Cells  are  the  hollow  ex- 
pansions of  the  alveolus  (Fig.  102). 
They  have    a   lining   of   very  fine  epi- 

_.    ,^-    „    ,.       ^     thelium,  without  cilia,  and  within  that 
Fig.  102.— Section  of  '  . 

an  alveolus,  show-  a  close  network  of  capillaries.     In  these 

mg  air  cells  open-  ^\^q  arteries  of  the  lung's  make  connec- 

ing  into  the  central  .            •  ^      ^           • 

cavity  tion  With  the  veins. 


Fig.  101.  — Two  alveoli,  show- 
ing the  clusters  of  air  cells. 


184  UNCONSCIOUS  NERVOUS   OPERATIONS 

259.  The  Lungs  are  made  ujd  of  collections  of  air  cells 
and  the  brandies  of  the  bronchial  tubes.  Their  texture 
is  spongy  and  elastic,  and  a  piece  of  a  lung,  unlike 
any  other  tissue,  will  float  in  water.  Each  lung  is  envel- 
oped in  the  pleura^  which  is  a  serous  membrane  folded 
back  to  form  the  lining  of  the  diaphragm  and  the  chest 
wall.  The  two  layers  of  the  pleura  are  in  contact  with 
each  other,  with  only  enough  of  the  fluid  secretion  to 
enable  them  to  glide  smoothly  over  each  other.  Each 
lung  is  partly  divided  into  lohes^  there  being  three  lobes 
in  the  right  and  two  in  the  left  lung  (Fig.  86).  Each  lobe 
is  also  made  up  of  many  small  parts  called  lobules,  each  con- 
taining a  minute  branch  of  a  bronchial  tube  with  air  cells, 
blood  vessels,  nerves,  and  lymphatics.  The  air  cells  in 
the  different  lobules  have  no  communication  with  one  an- 
other, so  that  if  one  of  the  bronchial  tubes  is  obstructed 
the  cells  opening  into  it  are  not  supplied  with  air. 

260.  Blood  supplied  to  the  Lungs.  —  The  blood  conveyed 
to  the  lungs  is  from  two  sources:  (1)  Tlie  pulmonary/ 
artery  from  the  right  ventricle  brings  the  impure  blood, 
collected  by  the  veins  throughout  the  body,  to  be  purified, 
or  oxygenated.  (2)  The  bronchial  arteries  bring  pure 
arterial  blood  for  the  nutrition  of  all  parts  of  the  organ. 
This  is  returned  through  the  bronchial  veins,  and  in  some 
measure  also  through  the  pulmonary  veins. 

261.  Inspiration  and  Expiration.  —  The  thorax  is  a  closed 
cavity,  and  the  air  cannot  reach  the  outside  of  the  lungs, 
hence  the  pressure  of  the  weight  of  the  atmosphere  affects 
the  lungs  only  from  the  inside,  and  they  are  kept  dis- 
tended to  fill  the  cavity.  If  the  thorax  is  increased  in 
size,  the  air  rushes  in  and  distends  the  elastic  cells  of  the 
lungs  still  more.  If  the  cavity  of  the  thorax  is  reduced 
in  size,  the  air  is  forced  out,  and  the  lungs  are  contracted. 


RESPIRATION 


185 


It  is  the  pressure  of  the  atmosphere  which  causes  the  air 
to  enter  the  lungs  in  what  is  called  inspiration^  and  the 
pressure  upon  the  lungs  by  the  walls  of  the  thorax  which 
forces  it  out  in  expiration.  These  two  acts  together  con- 
stitute respiration. 

262.  The  Respiratory  Mechanism.  —  In  respiration  the  size 
of  the  thorax  is  increased  in  two  ways:  (1)  by  the  de- 
pression of  the  diaphragm,  which  forms  the  floor  of  the 
cavity  and  separates  it  from  the  cavity  of  the  abdomen; 
(2)  by  the  elevation  of  the  forward  ends  of  the  ribs. 

263.  The  Diaphragm  is  a  sheet  of  muscle  and  tendon, 
convex  on  its  upper  side,  and  attached  by  bands  of  striped 
muscle  to  the  lower  ribs  at 

the  side,  to  the  sternum  and 
to  the  cartilages  of  the  ribs 
which  join  it  in  front,  and 
at  the  back  by  very  strong 
bands  to  the  lumbar  verte- 
brse.  Its  center  is  a  thin  ex- 
panse of  tendon.  When  the 
muscles  about  the  circumfer- 
ence contract,  the  arch  is  flat- 
tened upon  the  contents  of  the 
abdomen,  which  yield  to  its 
pressure,  and  the  thorax  is  en- 
larged downward  (Fig.  103). 

264.  Action  of  the  Ribs  and 
Muscles  of  the  Chest.  —  The 
ribs  are  attached  to  the  spinal  column  at  an  angle  smaller 
than  a  right  angle  (Fig.  33,  p.  45),  and  sloj^e  downw^ard 
toward  the  breastbone,  the  lower  ribs  sloping  more  than 
the  upper.  When,  by  the  contraction  of  the  chest  mus- 
cles, the  sternum  is  drawn  upward  and  outward,  the  ribs 


Fig.  103.  —  Diagram  illustrating 
the  varying  position  of  the  dia- 
phragm during  respiration. 


186  UNCONSCIOUS   NERVOUS   OPERATIONS 

are  raised  to  a  more  nearly  horizontal  position,  and  the 
cavity  they  inclose  is  enlarged  toward  the  front.  At  the 
same  moment  the  ribs  are  rotated  slightly  at  their  articula- 
tion with  the  vertebrse,  and  by  their  curvature  they  enlarge 
the  chest  at  the  sides.  Many  muscles  are  involved  in  this 
complex  action.  The  external  intercostal  muscles  (the 
elevators  of  the  ribs)  and  the  muscles  in  the  walls  of  the 
abdomen  are  principally  concerned,  but  certain  muscles 
of  the  head,  neck,  and  back  also  assist,  and  in  forced 
breathing  many  others  are  brought  into  use.  In  ordinary, 
quiet  expiration,  the  elasticity  of  the  chest  walls,  the 
cartilages,  and  the  lungs  is  sufficient  to  expel  the  air 
inhaled  without  special  muscular  contraction.  But  in 
sjDecial,  extraordinary  efforts  of  expiration,  as  in  cough- 
ing, sneezing,  singing,  etc.,  active  muscular  effort  is 
required.  For  this  purpose  the  muscles  of  the  abdominal 
walls  are  chiefly  brought  into  action,  and  by  them  the 
diaphragm  is  forced  upward,  the  cavity  of  the  thorax  is 
made  smaller,  and  the  air  is  driven  rapidly  out  of  the 
lungs.  When  those  muscles  again  relax,  the  chest  returns 
to  its  normal  size. 

265.  Effect  of  Respiration  upon  Air  in  the  Lungs.  —  The 
lungs  are  always  full  of  air,  about  two  hundred  cubic 
inches  remaining  in  the  lungs  of  an  adult  man  after 
expiration.  He  draws  in  and  breathes  out  in  ordinary 
breathing  from  twenty  to  thirty  cubic  inches,  and  in 
forced  respiration  may  take  in  and  expel  one  hundred 
cubic  inches  more.  By  what  is  known  as  the  diffusion  of 
gases  the  inspired  air  is  equally  mixed  throughout  with 
that  remaining  in  the  air  cells  and  tubes  of  the  lungs,  and 
there  is  no  accumulation  anyAvhere  of  air  which  has  been 
deprived  of  oxygen.  A  similar  interchange  takes  place 
through  the  walls  of  the  capillaries  between  the  gases  in 


RESPIRATION  187 

the  air  of  the  lungs  and  those  in  the  blood;  and  in  the 
same  way  the  oxygen  passes  from  the  blood  to  the  tis- 
sues, while  the  carbonic  acid  passes  from  the  tissues  into 
the  blood. 

266.  Atmospheric  Air  compared  with  Expired  Air.  —  The 
atmosphere  is  composed  of  five  gases :  oxygen,  nitrogen, 
argon,  carbon  dioxide,  and  watery  vapor,  the  last  varying 
greatly  in  relative  amount  according  as  the  atmosphere  is 
moist  or  dry.  Helium  and  other  recently  discovered 
gases  exist  in  the  air  in  very  small  traces,  but  may  be  left 
out  of  consideration.  Oxygen  and  nitrogen  are  the  prin- 
cipal elements  in  air.  The  amount  of  carbon  dioxide  in 
outdoor  air  is  very  small. 

Pure  dry  air  contains  in  each  one  hundred  parts  20.96 
parts  of  oxygen,  78  parts  of  nitrogen,  1  part  of  argon,  and 
.04  part  of  carbon  dioxide.  Expired  air  (breathed  once) 
contains  about  16  parts  by  volume  of  oxygen,  79  parts 
nitrogen  and  argon,  and  4  parts  carbon  dioxide.  There  is, 
besides,  in  expired  air,  a  considerable  quantity  of  watery 
vapor,  and  a  variable  amount  of  volatile  organic  matter, 
not  sufficient  generally  for  chemical  analysis  to  detect,  but 
often  perceived  in  a  close  room  by  the  sense  of  smell. 

It  appears  from  the  above  that  more  than  four  parts  of 
the  oxygen  is  appropriated  from  the  air  in  the  lungs,  and 
that  about  four  parts  of  carbon  dioxide,  besides  a  minute 
amount  of  organic  v^aste  and  some  vapor  of  water,  are 
given  back  to  the  air.  The  temperature  of  the  expired 
air  is  very  nearly  the  same  as  that  of  the  body. 

267.  Effect  of  Respiration  on  the  Blood.  —  The  blood 
brought  to  the  lungs  by  the  pulmonary  artery  is  dark 
purple  in  color,  but  that  which  is  returned  to  the  left 
auricle  of  the  heart,  after  circulating  through  the  lungs, 
is  of  a  brilliant  scarlet.      The    same    difference   is  seen 


188  UNCONSCIOUS   NERVOUS   OPERATIONS 

between  the  bright  arterial  blood  in  the  arteries  and  the 
dark  venous  blood  of  the  veins  of  the  systemic  circulation. 
Chemical  analysis  shows  that  this  difference  in  the  blood 
corresponds  to  the  difference  between  the  air  inspired  and 
the  air  expired.  The  immense  amount  of  capillary  sur- 
face which  the  air  reaches  in  the  air  cells  of  the  lungs  has 
taken  from  it  a  large  amount  of  oxygen  and  has  given  up 
to  it  carbon  dioxide  and  organic  waste,  together  with 
some  of  the  water  in  the  venous  blood  of  the  capillaries. 
That  is,  the  blood  has  been  arterialized  in  the  lungs,  for 
(except  in  the  pulmonary  circulation,  where  the  reverse  is 
the  case)  the  arteries  convey  the  oxygenated,  or  purified, 
nourishing  blood,  while  the  veins  are  filled  with  the  im- 
pure, partly  deoxidized,  and  poisonous  blood.  In  health 
both  arterial  and  venous  blood  contain  both  oxygen  and 
carbon  dioxide,  the  proportion  of  oxygen  being  much 
larger  in  the  arterialized  blood. 

268.  Function  of  the  Red  Corpuscles.  —  It  was  stated  in 
the  chapter  on  the  Blood  that  the  special  function  of  the 
red  corpuscles  is  to  take  up  and  hold  for  a  time  a  certain 
amount  of  oxygen,  and  then  to  give  it  up  to  other  tissues. 
The  red  corpuscles,  as  we  have  seen,  are  chiefly  made  up 
of  a  red  substance  called  hemoglobin,  and  hemoglobin 
which  has  absorbed  a  considerable  amount  of  oxygen 
becomes  oxyhemoglobin,  which  is  of  a  bright  scarlet  color. 
Oxyhemoglobin  becomes  hemoglobin  again  and  of  a  dark 
purplish  red  when  it  is  deprived  of  its  oxygen.  When 
brought  into  contact  with  air  in  the  lungs,  the  red  cor- 
puscles take  up  oxygen,  while  carbon  dioxide  is  given 
up  in  return.  The  oxygen  is  held  b}^  the  red  corpuscles 
in  loose  combination,  that  is,  in  such  a  chemical  union 
as  is  easily  disturbed,  the  oxygen  being  readily  given  up 
to  form  other  combinations. 


RESPIRATION  189 

269.  Tissue  Respiration.  —  The  lungs  were  once  regarded 
as  the  seat  of  the  combustion  of  the  body  —  as  the  fur- 
nace to  which  the  waste  of  the  body  was  brought  to  be 
burned  up.  It  is  now  known  that  the  tissues  themselves 
are  the  seat  of  combustion,  or  oxidation.  The  oxygen 
given  off  to  the  tissues  from  the  arterial  blood  in  the  cap- 
illaries is  not  necessarily  used  at  once  in  new  chemical 
combinations.  In  muscular  tissue,  and  probably  in  other 
varieties  of  tissue,  it  is  stored  for  future  use.  This  is 
shown  by  the  fact  that  severe  muscular  action,  by  which 
the  substance  of  the  muscle  fibers  is  broken  down  in  the 
production  of  energy,  results  in  the  elimination  of  carbon 
dioxide  which  contains  more  oxygen  than  the  whole 
amount  taken  up  by  the  lungs  during  the  time  of  action. 

It  appears  that  the  tissues  are  constantly  taking  oxygen 
from  the  blood  (or,  strictly  speaking,  from  the  lymph) 
and  combining  it  in  forms  which  are  easily  decomposed, 
and  thus  the  oxygen  is  ready  when  it  is  needed  for  the 
liberation  of  energy.  A  man  gives  off  from  his  lungs 
more  oxygen  in  the  form  of  carbon  dioxide  during  the 
day,  when  his  muscles,  brain,  and  digestive  organs  are 
at  work,  than  the  lungs  take  up  during  the  same  time. 
The  excess  had  been  stored  during  his  periods  of  rest. 
Although  oxygen  is  that  element  in  the  air  which  sup- 
ports life,  it  has  been  established  by  experiments  that  an 
animal  uses  no  more  oxygen  in  a  given  time  when  it 
breathes  the  gas  pure  than  when  it  breathes  ordinary  air, 
that  is,  the  amount  of  work  done  by  the  tissues  is  not  de- 
termined by  the  amount  of  oxygen  supplied  to  them,  but 
the  quantity  of  oxygen  used  is  determined  by  the  amount 
of  work  done.  An  excess  of  oxygen  above  that  amount 
needful  to  prevent  suffocation  will  not  make  the  organs 
work  any  more  than  extra  food  will  make  a  man  work. 

MACy's    PlIYS.  —  12 


190  UNCONSCIOUS   NERVOUS   OPERATIONS 

270.  Necessity  of  Ventilation.  —  In  each  ordinary  expira- 
tion of  an  adult  man,  from  twenty  to  thirty  cubic  inches 
of  air  issue  from  the  lungs,  or  in  one  hour  about  twelve 
cubic  feet.  This  air  has  been  deprived  of  a  large  pro- 
portion of  its  oxygen,  which  has  been  replaced  chiefly  by 
carbon  dioxide.  This  carbonic  acid,  while  not  itself  poi- 
sonous, at  least  in  small  quantities,  is  always  associated 
in  expired  air  with  waste  products  of  organic  life  which 
are  so,  and  is  a  measure  of  their  amount.  To  be  fit  for 
breathing,  air  should  not  contain  more  than  one  fifth  of  one 
per  cent  of  carbon  dioxide.  Some  authorities  say  one  tenth. 

It  is  found  that  in  quiet  breathing  a  man  gives  out 
something  over  1000  cubic  inches  of  carbon  dioxide  in  an 
hour.  If  hard  at  work,  he  will  expire  two  or  three  times 
as  much.  From  1000  to  3000  cubic  feet  of  fresh  air  per 
hour  for  each  occupant  of  a  closed  room  should  be 
supplied  from  outside  the  building,  and  in  hospitals  and 
workshops  the  amount  should  often  be  much  larger!  Per- 
sons vary  greatly  in  their  sensitiveness  to  impure  air. 
Many  become  accustomed  by  long  usage  to  dwelling  in 
ill-ventilated  rooms,  and  seem  to  suffer  no  immediate  evil 
effects  ;  when  others  coming  from  a  purer  atmosphere  will 
experience  dizziness,  headache,  or  nausea. 

271.  Ventilation  is  the  regular  and  continuous  removal 
of  the  expired,  vitiated  air  from  a  room  and  the  admis- 
sion of  pure  atmospheric  air.  To  be  adequate  to  human 
needs,  it  must  bring  into  a  room  enough  external  air  to 
dilute  the  poisonous  products  of  respiration  and  of  the 
combustion  of  gas,  oil,  or  candles,  together  with  the  exha- 
lations from  the  skin,  to  such  a  degree  that  the  air  of  the 
room  may  remain  pure  enough  for  breathing. 

The  amount  of  air,  by  weight,  inhaled  by  an  average 
person  in  twenty-four  hours  is   from  six  to  eight  times 


RESPIRATION  191 

that  of  the  food  which  he  eats,  and  it  is  at  least  quite  as 
important  that  this  air  shoukl  be  pure  as  that  the  food 
consumed  should  be  wholesome. 

Every  expiration  of  each  pair  of  lungs  in  a  closed  room 
reduces  the  quantity  of  oxygen  in  the  room  and  increases 
the  carbonic  acid  gas  and  other  impurities.  Now,  experi- 
ence and  experiment  have  proved  that  the  relative  propor- 
tions of  these  gases  in  the  air  inhaled  cannot  be  greatly 
changed  without  injuriously  affecting  animal  organisms. 
The  presence  of  1  per  cent  of  carbonic  acid  gas  is  harm- 
ful, though  1  per  cent  may  be  endured  for  a  time ;  but  it 
is  the  impurities  always  present  with  the  gas,  other  than 
the  carbonic  acid  gas  itself,  together  with  the  increase  of 
moisture  and  heat  and  unpleasant  odors ,  that  produce  the 
bad  effects.  When  the  amount  of  carbon  dioxide  becomes 
10  per  cent  death  is  only  a  matter  of  time. 

A  person  may  be  suffocated  to  death  in  an  ill-ventilated 
room  from  lack  of  oxygen,  from  an  excess  of  carbon 
dioxide,  or  from  the  two  causes  combined,  and  he  is  also 
exposed  to  other  dangers  whose  effects  are  not  manifest 
at  once.  If  several  persons  are  present,  germs  of  disease 
are  liable  to  be  floating  in  the  air  or  clinging  to  walls  or 
floor,  and  may  easily  be  drawn  into  the  lungs  along  with 
other  dust.  The  diseases  most  often  communicated  in 
this  way  are  consumption  and  pneumonia,  eacli  of  which 
is  believed  to  be  caused  by  a  specific  bacterium. 

272.  Methods  of  Warming  and  Ventilation. —  In  some  mod- 
ern buildings,  provision  for  ventilation  is  made  in  connec- 
tion with  the  heating  apparatus.  Hot  air  furnaces  provide 
for  a  constant  flow  of  warm  air  into  a  room,  with  the  removal 
of  that  already  present.  The  danger  is  lest  the  air  brought 
in  should  be  taken  not  from  pure  outdoor  sources  but  from 
cellars,  or  from  rooms  where  it  has  been  already  vitiated, 


192  UNCONSCIOUS  NERVOUS   OPERATIONS 

or  from  openings  too  near  a  cesspool  or  sewer  pipe. 
Houses  warmed  by  the  circulation  of  steam  or  hot  water 
must  have  independent  arrangements  for  ventilation  by 
means  of  open  fireplaces  or  chimney  flues,  and  adequate 
openings  for  admitting  pure  air.  The  same  may  be  said 
of  houses  heated  by  ordinary  air-tight  stoves,  or  by  oil 
and  gas  stoves.  The  latter,  while  making  no  provision  for 
ventilation,  increase  the  need  of  it  by  their  combustion. 

When  adequate  provision  for  ventilation  is  not  made  in 
the  construction  of  a  building,  fresh  air  may  be  admitted, 
without  causing  a  direct  draught,  by  fitting  a  board  six 
or  eight  inches  wide  under  a  raised  window  sash,  so  that 
the  exchange  between  internal  and  external  air  may  take 
place  between  the  sashes.  Such  an  arrangement  is  useful 
in  schoolrooms  and  other  places  of  assembly.  Care  should 
be  taken  to  avoid  a  draught  of  cold  air,  which  is  some- 
times more  immediately  dangerous  than  to  breathe  viti- 
ated air  for  a  little  while.  At  the  same  time  it 'should 
not  be  forgotten  that  the  worst  effects  of  breathing  im- 
pure air  do  not  appear  at  once.  While  it  is  a  direct  cause 
of  pulmonary  consumption  (the  greatest  scourge  of  the 
human  race)  and  other  ills,  it  may  be  a  long  time  before 
disease  appears.  The  vitality  of  the  system  is  gradually 
lowered,  strength  and  vigor  are  undermined,  so  that  some 
slight  overexertion  or  exposure  to  cold  or  to  specific 
germs  of  disease  may  result  in  serious  or  fatal  conse- 
quences. When  the  whole  system  is  kept  by  correct 
habits  of  life  at  a  high  level  of  health,  when  all  the  parts 
work  vigorously,  easily,  and  in  harmony,  one  is  able  to 
endure  unharmed  exposure  even  to  active  germs  of  malig- 
nant diseases. 

273.  Correct  Breathing.  —  One  can  breathe  properly  only 
when  the  clothing  is  loose  enough  to  allow  entirely  free 


RESPIRATION  193 

movement  of  all  the  muscles  concerned  in  respiration.  It 
has  been  noticed  that  men  and  infants  use  the  abdominal 
muscles  and  those  of  the  lower  part  of  the  chest  more 
than  women  do.  This  is  not  because  women  have  a 
sort  of  breathing  apparatus  different  from  that  of  other 
human  beings,  but  because  their  clothing  is  too  frequently 
worn  so  tight  that  full  and  free  respiration  is  impossible, 
the  various  organs  being  displaced  and  deformed,  and  the 
Avhole  s^-stem  weakened,  while  to  the  artistic  eye  the  fig- 
ure appears  distorted  and  ugly. 

One  should  accustom  himself  to  go  often  into  the  open 
air  and  draw  long,  full,  and  deliberate  breaths,  followed 
by  slow  expiration,  in  order  that  all  the  minute  air  cells 
of  the  lungs  may  be  filled  and  their  walls  expanded. 
Those  which  are  habitually  unused  may  become  perma- 
nently collapsed  and  hardened,  and  the  capacity  of  the 
lungs  be  thus  reduced,  the  whole  system  being  weakened 
and  prepared  to  fall  an  easy  prey  to  disease. 

274.  Temperature  of  Air  for  Breathing.  —  Man  is  able  to 
live  a  healthy  life  in  the  most  torrid  climates  and  in 
regions  where  the  air  is  many  degrees  below  the  freezing 
point.  He  can  even  remain  for  some  time  unharmed  in  a 
chamber  heated  far  above  the  boiling  point  of  w^ater. 
Such  are  the  marvelous  adjustments  of  which  his  organ- 
ism is  capable. 

But  in  connection  with  the  artificial  Avarming  of  closed 
rooms,  it  is  necessary  to  inquire  as  to  the  most  healthful 
temperature  of  the  air  habitually  breathed.  Most  people 
in  America  live,  in  winter,  in  rooms  too  hot  for  health, 
and  thus  render  themselves  unnecessarily  liable  to  ^^  take 
cold  "  on  going  out.  A  living  room  for  adults  in  ordinary 
health  should  have  a  temperature  of  from  65""  to  70°  F. 
(18°  to  21°  C).     For  young  children,  the  aged,  or  the 


194  UNCONSCIOUS   NERVOUS  OPERATIONS 

feeble  the  room  may  be  a  few  degrees  warmer.  Sleep- 
ing rooms  should  usually  be  much  colder,  but  definite 
rules  cannot  be  given.  Much  depends  upon  habit,  age, 
and  state  of  health.  To  live  always  in  a  warm  atmos- 
phere is  enervating.  Cold  air,  when  pure,  is  far  more 
refreshing  and  invigorating.  It  is  highly  desirable  to 
accustom  one's  self  to  sleep  with  open  windows  in  all 
seasons. 

275.  Respiration  as  affected  by  the  Use  of  Alcohol  and 
Tobacco.  —  The  action  of  alcohol  upon  the  muscular  walls 
of  the  arteries,  which  has  been  already  more  than  once 
referred  to,  is  especially  important  in  the  capillaries  of  the 
lungs.  When  they  are  dilated  by  the  paralyzing  effect 
of  alcohol,  their  expansion  reduces  the  size  of  the  air  cells 
in  the  lungs  and  leaves  less  room  for  the  air  which  the 
lungs  need,  so  that  less  oxygen  is  supplied  to  the  blood. 
When  the  capillaries  are  often  or  continuously  distended 
in  this  way,  their  walls  are  likely  to  become  permanently 
thickened,  and  the  interchange  of  gases  which  normally 
takes  place  there,  by  which  carbon  dioxide  passes  from 
the  blood  while  the  purifying  oxygen  is  taken  into  the 
blood,  is  impeded.  Serious  disease  even  may  result,  such 
as  a  peculiar  and  quickly  fatal  form  of  consumption  found 
only  among  drinkers  of  alcoholic  fluids. 

The  throat,  bronchial  tubes,  and  lungs  of  a  tobacco 
smoker  are  all  liable  to  irritation  by  the  poisonous  smoke, 
and  chronic  inflammation  is  often  caused.  The  nicotine 
of  tobacco  is  a  deadly  poison,  and  in  cigarettes  there  are 
often  other  poisons  equally  dangerous  to  health. 

Demonstrations  and  Experiments 

83.  Dissection  of  the  Respiratory  Organs. —  The  thorax  of  a  rabbit, 
cat,  or  dog  will  be  found  serviceable.     Before  cutting  open  the  chest, 


RESPIRATION 


195 


Tig.  104.— Apparatus 
to  illustrate  the 
action  of  the  dia- 
phragm in  respira- 
tion. 


the  arrangement  of  the  ribs,  intercostal  muscles,  and  connected  parts 
should  be  noticed.  When  the  thorax  is  cut  open  the  lungs  collapse. 
Observe  the  relation  of  the  heart  to  the  lungs.  Inflate  the  latter 
through  a  tube  inserted  in  the  trachea.  Observe  the  diaphragm  ; 
note  its  shape  in  contraction  and  relaxation.  Cut  open  the  lungs  and 
trace  out  in  them  the  subdivisions  of  the  bronchial  tubes.  The  struc- 
ture of  the  trachea  and  larynx  should  be  carefully  studied. 

84.  To  illustrate  the  A  ction  of  the  Diaphragm  in  Respiration.  —  Tie 
over  the  large  end  of  a  stoppered  bell  jar,  or  of  a  large  bottle  whose 

bottom  has  been  removed,  a 
piece  of  thin  rubber  cloth 
(Fig.  104).  Close  the  smaller 
opening  of  the  jar  with  a 
cork,  through  which  runs  a 
glass  tube,  on  whose  inner  end 
a  thin  rubber  bag  is  tied,  as 
shown  in  the  figure.  Then,  if 
the  rubber  bottom  be  pushed 
in,  the  bag  will  collapse. 
When  the  bottom  is  allowed 
to  return  to  its  first  position, 
the  bag  expands.  The  rub- 
ber bottom  represents  the  dia- 
phragm, and  the  small  rubber 
bag  and  the  glass  tubing  the 
lungs  and  trachea,  while  the 
jar  itself  represents  the  tho- 
rax. If  the  lungs  and  trachea  of  a  small  animal  be 
carefully  dissected  out,  they  may  be  used  to  replace 
the  small  rubber  bag  by  tying  the  glass  tube  in  the 
trachea.  In  this  way  may  be  shown  the  movements 
of  the  lungs  themselves  in  respiration.  Another  form 
of  apparatus  for  demonstrating  the  action  of  the 
diaphragm  in  respiration  is  shown  in  Fig.  105,  in 
which  the  bell  jar  and  rubber  cloth  of  Fig.  104  are 
replaced  by  a  lamp  chimney  and  a  piston.  (The 
piston  can  be  made  of  a  wooden  stick  with  a  piece 
of  wet  cloth  tied  around  the  large  end.) 

85.  To  illustrate  the  Function  of  the  Ribs  in  Respiration.  —  Construct  a 


Tig.  105. 

Apparatus  to  de- 
monstrate the 
action  of  the 
diaphragm  in 
respiration. 


196 


UNCONSCIOUS  NERVOUS  OPERATIONS 


piece  of  apparatus  as  shown  in  Fig.  106.  The  standard  AB  repre- 
sents the  vertebral  column  ;  the  two  pieces  CD  and  EF  represent  two 
of  the  ribs,  wath  DF,  a  portion  of  the  sternum,  attached ;  a  and  b  are 
rubber  bands  representing  the  external  and  internal  intercostal  muscles 
respectively ;    c  is  a  rubber  band  of  such  strength  that  it  keeps  the 


Fig.  106.  — Apparatus  to  illustrate  the  movements  of  the  ribs  and 
sternum  in  respiration. 


apiDaratus  in  position  I  when  the  rubber  bands  a  and  b  are  both  on. 
Remove  the  rubber  band  a ;  DFis  lowered.  Replace  a  and  remove  b ;  DF 
is  raised.  Observe  that  when  DF  is  raised  from  position  II,  the  dis- 
tance between  DF  and  CE  is  increased,  unless  DF  is  raised  too  far. 

86.  To  show  the  Moisture  in  Respired  A ir.  —  Breathe  upon  a  cool  plate 
of  glass ;  some  of  the  vapor  in  the  breath  will  be  condensed  upon  the 
glass.  To  show  that  the  presence  of  moisture  is  due  to  respiration, 
blow  upon  the  glass  with  bellows. 

87.  To  show  that  Air  is  made  Warmer  in  Respiration.  —  !N"oticethe 
reading  of  a  thermometer,  then  breathe  upon  its  bulb. 

88.  Some  Properties  of  the  Constituent  Gases  of  Air.  —  The  teacher 
should  prepare  oxygen,  nitrogen,  and  carbon  dioxide  by  methods 
given  in  ordinary  text-books  of  chemistry.  Place  a  smoldering 
splinter  of  wood  in  a  vessel  of  oxygen ;  the  stick  bursts  into  flame. 
Place  the  flaming  splinter  in  a  vessel  of  carbon  dioxide  or  nitrogen  ; 
the  flame  is  at  once  extinguished.  Place  a  blazing  splinter  in  an 
empty  jar,  i.e.  containing  only  air;  after  burning  some  time  it  goes 
out.  Before  the  last  trace  of  fire  disappears,  transfer  the  splinter  to 
a  jar  of  oxygen;  it  burns  actively  again.  Into  a  clean,  empty  jar  put 
a  little  limewater,  prepared  by  dissolving  lime  in  water.  Cover  the 
jar  and  shake  it  well;  if  any  considerable  amount  of  carbon  dioxide  is 
present,  a  w^hite  precipitate  will  form  in  the  limewater.  Now  place 
a  burning  splinter  in  the  jar  and  allow  it  to  burn  out.     Then  shake 


RESPIRATION  197 

the  jar  ;  the  presence  of  carbon  dioxide  will  be  very  evident.  Repeat 
the  latter  operation  after  allowing  splinters  to  burn  out  in  a  jar  of 
oxygen.  From  these  experiments  it  becomes  evident  that  oxygen  is 
necessary  in  ordinary  combustion,  and  that  carbon  dioxide  is  a 
product  of  combustion. 

89.  To  show  that  Respiration  increases  the  A?nount  of  Carbon  Diox- 
ide in  the  Air. — By  means  of  a  glass  tube  blow  through  limewater; 
the  white  precipitate  of  carbonate  of  lime  shows  the  presence  of  car- 
bon dioxide  in  the  breath.  To  show  that-most  of  this  is  a  product  of 
respiration,  pass  some  of  the  ordinary  air  of  the  room  through  lime 
water ;  the  white  precipitate  is  much  smaller  in  amount. 

90.  To  illustrate  a  Difference  between  ^'Arterial"  and  ^^  Venous" 
Blood.  —  Obtain  some  fresh  ox  blood  at  a  slaughterhouse  and  "whip" 
it  to  remove  the  fibrin  and  prevent  clotting.  By  means  of  a  carbon 
dioxide  generator,  pass  carbon  dioxide  gas  through  the  blood ;  the 
blood  becomes  darker.  I^ow  pass  air  through  it,  thus  supplying 
oxygen ;  it  becomes  more  scarlet  in  color. 


CHAPTER  XY 
NERVOUS   CONTROL  OF  THE   RESPIRATORY  APPARATUS 

276.  The  movements  of  respiration  may  go  on  in  ordi- 
nary quiet  breathing  without  consciousness  and  without 
volition,  but  they  are  also,  in  a  measure,  under  voluntary 
control  —  not  wholly  so,  for  it  is  impossible  to  commit 
suicide  by  holding  the  breath. 

277.  The  Respiratory  Center  and  Nerves  (Fig.  107).  —  A 
certain  restricted  area  in  the  medulla  oblongata  is  recog- 
nized as  the  respiratory  center^  and  there  are  believed  to 
be  other  such  centers  lower  down  in  the  spinal  cord.  Nerv- 
ous impulses  pass  from  the  center  down  the  spinal  cord, 
and  thence  by  the  anterior  roots  of  many  of  the  spinal 
nerves  to  the  plexuses  which  those  nerves  form.  By  com- 
municating branches  from  these  plexuses  connection  is 
made  with  the  spinal  ganglia  of  the  sympathetic  system, 
and  with  the  tenth  and  eleventh  cranial  nerves.  From 
these  various  sources  motor  fibers  pass  on  to  the  numerous 
muscles  concerned  in  respiration.  That  which  supplies 
the  diaphragm  is  the  phrenic  nerve^  which  is  traced  back 
to  the  three  or  four  upper  pairs  of  spinal  nerves. 

If  the  spinal  cord  be  divided  below  the  fourth  pair  of 
spinal  nerves,  the  diaphragm  will  continue  to  act,  but  the 
intercostal  muscles  will  be  paralyzed.  If  the  cord  be  cut 
just  below  the  medulla  oblongata,  all  respiratory  movement 
of  the  chest  ceases ;  and  if  that  small  portion  of  the  medulla 

198 


NERVOUS  CONTROL  OF  RESPIRATORY  APPARATUS       199 


oblongata  known  as  the  respiratory  center  be  removed,  no 
further  respiratory  movements  will  take  place,  and  death 
immediately  follows. 
On  the  other  hand,  the 
whole  of  the  brain  for- 
ward of  the  medulla 
may  be  removed,  and 
breathing  will  not  stop. 
278.  The  Expiratory 
Center.  —  It  is  now  un- 
derstood that  the  cen- 
ter of  respiration  in 
the  medulla  is  in  real- 
ity double, — that  there 
is  one  center  for  inspir- 
atory movement  and 
another  beside  it  for 
expiratory  movement. 
In  ordinary  quiet 
breathing  the  first  only 
is  excited,  expiration 
taking  place  by  the  re- 
laxation of  the  muscles 
contracted  in  inspira- 
tion. But  in  violent  or 
forced  expiration  the 
internal  intercostal  and 
abdominal  muscles  are 
brought  into  active  use, 
and  the  nervous  influ- 
ence stimulating  them 
to  action  comes  from 
the  expiratory  center. 


Fig.  107. —  Diagram  of  the  nervous  con- 
trol of  the  respiratory  organs. 

ab  motor  spinal  nerves  going  to  muscles  of 
the  abdominal  walls. 

E     expiratory  center. 

ex  sensory  nerve  fibers  from  the  larynx  ex- 
citing the  expiratory  center, 

ex'  sensory  fibers  from  the  lungs  exciting 
the  expiratory  center. 

ex^  motor  spinal  nerve  fibers  passing  to 
external  intercostal  muscles. 

I      inspiratory  center. 

in  sensory  fibers  from  larynx  inhibiting 
the  inspiratory  center. 

in'  sensory  fibers  from  the  lungs  that  excite 
the  inspiratory  center. 

int  motor  spinal  nerve  fibers  passing  to  in- 
ternal intercostal  muscles. 

ph  motor  fibers  of  phrenic  nerve  going  to 
diaphragm. 


200  UNCONSCIOUS  NERVOUS   OPERATIONS 

279.  Reflex  Action  of  Respiratory  Center.  —  Though  the 
action  of  the  breathing  center  in  the  medulla  oblongata  is 
shown  by  experiment  to  originate  efferent  nervous  impulses 
independent  of  irritation  conveyed  to  it  by  sensory  fibers, 
it  is  also  largely  under  reflex  control.  For  instance,  when 
the  mucous  membrane  of  the  air  passages  is  irritated  by 
foreign  substances,  a  sudden  sneeze  or  cough  results.  A 
sudden  dash  of  cold  water  upon  the  skin  causes  a  quick, 
long  inspiration.  So  it  appears  that  in  normal  respiration 
the  movements  are  not  reflex,  while  reflex  movements  are 
also  possible. 

280.  The  Normal  Excitation  of  the  Respiratory  Center  is  due, 
more  than  to  any  other  cause,  to  the  relative  amounts  of 
oxygen  and  carbon  dioxide  in  the  blood  which  reaches  it. 
If  the  blood  contains  too  little  oxygen  and  too  much  carbon 
dioxide,  the  center  is  stimulated,  and  the  resulting  respira- 
tory movements  tend  to  correct  the  evil. 

Afferent  nervous  influences  brought  to  the  center  along 
the  vagus  nerves  also  excite  its  action.  The  main  trunk 
of  this  tenth  nerve  contains  fibers  which  excite  inspiration, 
and  other  fibers  which  inhibit,  or  check,  inspiratory  move- 
ments. It  is  supposed  that  the  expansion  of  the  air  cells 
in  the  lungs,  where  many  of  the  vagus  fibers  end,  produces 
impulses  along  those  fibers  which  result  in  inhibitory  or 
expiratory  impulses  from  the  center  in  the  medulla  ;  while, 
on  the  other  hand,  collapse  of  the  air  cells  excites  along 
other  fibers  contrary  impulses  which  result  in  inspiration. 
Thus  the  action  of  the  lungs  becomes  that  of  a  self-i'egulat- 
ing  pump.  Other  afferent  impulses  along  branches  of  the 
vagus,  or  from  other  nerve  fibers  connected  with  it,  may 
also  affect  respiration. 


CHAPTER   XVI 

FOOD 

281.  Losses  of  the  Body.  —  One  effect  of  respiration  is  to 
reduce  the  weight  of  the  body.  A  man  gives  off  from 
the  lungs,  in  the  course  of  twenty-four  hours,  about  eight 
ounces  of  carbon  and  about  half  a  pint  of  water,  Avhich 
are  taken  from  the  tissues  of  the  body  as  worn-out  mate- 
rials. There  are  also  other  sources  of  loss  to  the  body  in 
the  processes  of  excretion,  by  which  the  waste  or  used-up 
matter  of  the  body  is  cast  off. 

282.  Sources  of  Restoration.  —  These  losses  must,  of 
course,  be  made  good,  or  the  body  will  Avaste  away. 
Through  the  lungs  we  get  oxygen  only,  while  we  need 
hydrogen,  nitrogen,  carbon,  and  other  chemical  elements 
besides,  which  enter  into  the  composition  of  our  bodies. 
These  come  to  us  in  the  food  which  we  eat,  and  are  pre- 
pared for  use  Avithin  the  body  by  the  process  called 
digestion. 

Food  is  that  which,  taken  into  the  alimentary  canal,  sup- 
plies material  for  the  grotcth  and  repair  of  tissue,  for  the 
generation  of  force,  or  for  the  regulation  of  force. 

283.  Nutrition.  —  Digestion  is  but  one  portion  of  a  com- 
plicated series  of  processes,  called  nutrition,  AAhich  result 
in  the  groAA'th  and  repair  of  the  constantly  wasting  tissues. 
In  its  broad  sense  nutrition  includes  respiration,  Avhicli 
supplies  the  oxygen  needed;   digestion,  or  the  conversion 

201 


202  UNCONSCIOUS  NERVOUS   OPERATIONS 

of  food  by  the  chemical  action  of  the  digestive  juices  into 
soluble  substances  ready  to  be  acted  upon  by  the  absorb- 
ents; absorption^  or  the  passage  of  selected  elements  from 
the  digested  food  through  the  walls  of  the  blood  vessels 
and  lymphatics  (lacteals);  assimilation^  or  the  conversion 
of  the  new  particles  of  food  into  the  substance  of  the 
tissues  of  the  body;  and  the  breaking  down  of  the  sub- 
stance of  the  tissues  to  form  waste.  The  building-up 
processes  constitute  what  is  called  anaholism,  the  break- 
ing down  of  tissue  katabolism,  while  the  whole  double 
operation  receives  the  scientific  name  of  metabolism.  We 
are  now  to  study  anabolism. 

284.  Object  of  Nutrition.  —  The  various  processes  of  nu- 
trition take  place  in  order  to  supply  the  human  machine 
with  material  in  suitable  form  for  the  production  of 
energy.  The  oxidizable  substances  are  distributed  to 
the  tissues  and  are  there  submitted  to  the  action  of  the 
oxygen  in  the  blood.  Combustion  then  takes  place,  that 
is,  the  substances  in  the  tissue  cells  are  burned.  The 
complex  chemical  compounds  there  found  are  decomposed, 
and  new  and  simpler  compounds  are  formed,  which  being 
of  no  further  use  to  the  body  are  removed  from  it  by 
mechanisms  prepared  for  the  purpose. 

285.  Forms  of  Energy  in  the  Body.  —  The  force  set  free 
in  the  tissues  by  the  combustion  of  their  particles  takes 
many  forms  within  the  body,  but  as  it  leaves  the  body  it 
appears  in  two  forms  only  :  as  heat  or  as  work  done  by 
the  muscles.  Just  as  matter  may  be  changed  from  one 
form  to  another,  but  cannot  be  destroyed,  so  energy,  or 
force,  may  be  changed  from  one  form  to  another,  but  can- 
not be  destroyed.  The  heat  driven  off  in  the  combustion 
of  coal  may  be  changed  through  the  agency  of  steam  into 
the   motion  of   machinery,  which  may   in   turn   be  con- 


FOOD  203 

verted  into  electrical  force  or  light,  or  again  become  heat. 
A  mechanic's  blow  upon  an  anvil  converts  muscular  force 
into  motion,  heat,  and  light.  Any  form  of  energy  must 
result  from  some  other  form  of  energy.  It  cannot  come 
from  nothing. 

286.  Conservation  of  Energy  and  Correlation  of  Forces.  — 
These  facts,  in  works  uj^on  the  science  of  physics,  are 
stated  as  the  laws  of  conservation  of  energy  and  of  the 
correlation  of  forces.  The  human  body,  like  all  other 
matter,  is  subject  to  these  laws. 

As  the  power  for  a  large  proportion  of  our  machines 
comes  from  the  heat  of  combustion,  —  that  is,  the  union 
of  oxygen  with  other  matter,  —  so  does  the  energy  of  the 
body  come  mainly  from  the  same  chemical  action,  and  the 
products  of  the  slow  combustion  of  food  which  takes  place 
within  the  body  are  much  the  same  as  they  would  be  if 
the  food  were  burned  in  a  furnace  by  swift  combustion. 
Those  products  are  carbon  dioxide,  water,  and  a  nitrogen- 
containing  substance  which  is  discharged  from  the  body 
as  urea,  besides  certain  salts  not  oxidizable  which  would 
appear  in  the  furnace  as  ashes. 

287.  Food  Elements.  —  The  valuable  parts  of  the  matter 
which  we  call  food  enter  in  varying  proportions  into  many 
different  articles  which  we  eat.  Chemists  divide  these 
elements,  which  are  essential  to  the  maintenance  of  the 
body  in  health,  into  five  classes,  as  follows  :  — 

1.  Proteids  (Nitrogenous  foods)  1 

2.  Carbohydrates    )      ,„       .,  .       \    Ore-aiiic 
3_   -p^^g                      \     (Nonnitrogenous)  ^'^ 

4.  Water     ) 

5.  Salts        f  Inorganic 

Milk  and  eggs  are  examples  of  food  containing  all 
these  materials  in  proportions  suitable  for  young,  grow- 


204  UNCONSCIOUS   NERVOUS   OPERATIONS 

ing  animals,  and  they  are  therefore  spoken  of  as  "  perfect 
foods." 

288.  Characteristics  of  a  Healthful  Diet.  —  (1)  A  health- 
ful diet  must  contain  all  five  chemical  classes  of  food 
elements  in  due  proportion.  (2)  It  must  be  adapted  to 
the  climate,  to  the  age  of  the  individual,  and  to  his  mode 
of  life,  that  is,  to  the  kind  and  amount  of  work  which 
he  does.  (3)  Not  only  must  the  different  kinds  and 
amounts  of  necessary  food  appear  in  the  diet,  but  they 
must  appear  in  digestible  form. 

289.  Classification  of  Foods.  —  With  reference  to  the  use 
made  of  them,  foods  are  divided  into  three  classes  :  (1) 
tissue  builders  ;  (2)  force  generators  ;  (3)  force  regu- 
lators. The  proteids  constitute  the  first  class,  though 
we  are  not  certain  but  that  they  may  be  sometimes  oxi- 
dized, yielding  force  without  having  entered  into  the 
composition  of  living  cells.  In  the  second  class  are, placed 
the  oxidizable  substances,  —  the  fats  and  carbohydrates. 
They  may  also  assist  in  forming  tissue  to  some  extent. 
The  third  class  includes  the  inorganic  compounds,  — 
water,  salts,   etc., — and  certain /ooc?  accessories. 

290.  Proteids  are  the  most  important  substances  which  en- 
ter into  the  animal  organism,  being  absolutely  essential  to 
the  phenomena  of  life.  Plants  are  the  great  manufacturers 
of  jDroteids;  no  process  has  yet  been  discovered  for  making 
them  artificially.  Proteids  are  complex  chemical  com- 
pounds and  are  characteristically  represented  by  the 
casein  of  milk  and  the  albumin  of  Qgg.  All  are  com- 
jjosed  of  carbon,  hydrogen,  nitrogen,  and  oxygen  in 
various  proportions,  with  a  trace  of  sulphur.  Proteids 
are  the  only  group  of  foods  which  contain  nitrogen,  and 
whose  chief  if' not  sole  purpose  is  the  building  of  tissue. 
Animals  can  live  without  carbohydrates  and  fats,  but  not 


FOOD  205 

without  proteids.  The  chief  proteids  are  the  gluten 
of  all  cereals,  peas,  potatoes,  beans,  and  lentils;  the  albu- 
min in  white  of  Qgg,  milk,  and  blood;  globulin  from  yolk 
of  Qgg  and  blood;  myosin  found  in  lean  meat;  casein  in 
milk  and  cheese:  fibrin  in  clotted  blood.  Though  certain 
vegetables  (as  beans  and  peas)  contain  more  proteid  than 
does  meat,  they  furnish  it  in  a  less  digestible  form,  that 
is,  a  considerable  part  of  it  passes  from  the  bod}'  unaf- 
fected by  the  digestiye  processes,  and  the  proteid  of  these 
vegetables  is  therefore  less  valuable  as  food. 

Since  only  the  proteids  contain  nitrogen,  they  are  called 
nitrogenous  foods ;  and  carbohydrates  and  fats  are  called 
nonnitrogenous. 

A  healthy,  well-fed  animal  is  found  to  lose  by  excretion 
as  much  nitrogen  daily  as  is  supplied  in  his  food.  If  the 
food  contains  an  insufficient  amount  of  nitrogen,  the  quan- 
tity excreted  is  greater  than  that  received,  and  the  tissues 
waste  away. 

291.  Fats  are  found  in  butter,  milk,  cheese,  and  meat, 
in  some  of  the  grains,  and  in  oils.  They  contain  carbon, 
hydrogen,  and  oxygen.  They  are  oxidized  in  the  body, 
and  furnish  energy  and  heat. 

292.  The  Carbohydrates,  like  the  fats,  contain  carbon, 
hydrogen,  and  oxygen;  but  the  proportion  of  oxygen  is 
larger  than  in  fats.  The  carbohydrates  include  (1)  starchy 
which  is  found  in  cereals,  vegetables,  nuts,  etc.;  (2)  sugars 
of  different  kinds, —  grape  sugar,  cane  sugar,  malt  sugar, 
and  milk  sugar,  besides  sugar  manufactured  from  starch; 
and  (3)  cellulose,  found  in  fruits,  cereals,  and  all  vegetables. 
Carbohydrates  are  very  rapidly  oxidized  in  the  body,  pro- 
ducing heat,  and  it  is  they  that  are  used  up  in  the  setting 
free  of  energy  when  the  muscles  are  vigorously  exercised; 
for  it  is  found  that  the  nitrogenous  waste  does  not  increase 

macy's  piiys.  — 13 


206  UNCONSCIOUS  NERVOUS   OPERATIONS 

in  proportion  to  the  increase  of  muscular  effort.  Carbo- 
hydrates cannot  alone  form  tissue,  but  under  some  circum- 
stances may  be  used  for  that  purpose  with  other  elements. 

293.  Water,  composed  of  oxygen  and  hydrogen,  is  found 
in  all  foods,  and  has  a  variety  of  uses  in  connection  with 
nutrition,  partly  as  a  solvent  for  various  elements  in  the 
food,  and  partly  as  promoting  osmosis,  and  as  an  aid  to 
the  varied  changes  which  take  place  in  the  tissues.  Water 
uncombined  with  food,  introduced  into  the  stomach  as  in 
drinking,  is  all  absorbed  directly  into  the  blood,  of  which 
it  forms  about  80  per  cent. 

294.  Salts.  —  The  food  elements  that  are  salts  are  chiefly 
the  chlorides,  phosphates,  and  carbonates  of  sodium  and 
potassium,  and  to  a  less  extent  those  of  calcium  and  mag- 
nesium, with  salts  of  iron  and  of  some  of  the  organic  acids. 
Common  salt  (chloride  of  sodium)  appears  in  all  animal 
bodies,  and  to  some  extent  in  plants  also.  It  helps  to  dis- 
solve certain  of  the  albumins  of  the  body,  promotes  the  flow 
of  the  digestive  fluids,  and  aids  digestion  in  various  ways. 
About  half  an  ounce  each  day  is  needed  with  the  food. 
That  these  saline  matters  are  essential  to  health,  is  proved 
by  experiments  upon  animals.  When  they  are  eliminated 
so  far  as  possible  from  the  diet,  the  central  nervous  sys- 
tem soon  suffers,  and  paralysis  results,  besides  general 
derangement  of  nutrition.  When  an  animal  body  is 
burned,  the  various  salts  which  entered  into  its  composi- 
tion appear  in  the  ashes  Avhich  are  left,  while  the  other  sub- 
stances have  been  changed  into  gases. 

295.  Food  Accessories.  —  These  are  the  various  drinks  — 
alcohol  in  different  forms,  tea,  coffee,  cocoa,  etc. ;  and  condi- 
ments —  mustard,  pepper,  ginger,  and  other  spices,  and  a 
variety  of  other  flavors  added,  not  for  their  food  value 
(though  of  that  they  may  liave  a  small  amount),  but  to  give 


FOOD  207 

a  pleasant  taste  which  may  assist  digestion,  and  to  stimulate 
the  secretion  of  digestive  juices.  Used  to  excess,  how- 
ever, all  these  drinks  injuriously  affect  the  nerves,  and 
the  condiments  may  irritate  the  sensitive  lining  membrane 
of  the  alimentary  canal,  besides  impairing  the  delicacy  of 
the  sense  of  taste. 

296.  Food  Values.  —  The  nutritive  value  of  a  diet  lies 
chiefly  in  the  amount  of  nitrogen  and  carbon  derived  from 
it.  A  man  of  moderately  active  life  will  give  off,  mainly 
from  the  lungs  as  carbon  dioxide,  from  eight  to  nine 
ounces  of  carbon  each  day.  If  he  is  engaged  in  severe 
muscular  effort,  he  will  give  off  much  more  carbon.  The 
amount  of  nitrogen  passing  from  the  body  (chiefly  as  urea) 
during  a  day  is  from  .47  to  .56  ounce,  and  with  the 
increase  of  muscular  activity  it  does  not  increase  to  nearly 
so  great  a  degree  as  does  the  carbon. 

In  order  to  repair  the  daily  waste  of  the  tissues,  the 
proportions  of  carbon  and  nitrogen  contained  in  the  food 
should  be  the  same  as  in  the  excretions,  viz.  about  16.6  to 
1.  While  the  proteids  contain  carbon,  they  contain  only 
about  3.5  parts  of  carbon  to  1  of  nitrogen,  hence  other 
groups  of  food  elements  must  be  depended  upon  to  supply 
the  necessary  carbon. 

The  oxygen  contained  in  food,  being  already  combined 
with  other  elements,  cannot  be  used  in  oxidation,  so  that 
from  the  lungs  alone  comes  the  needful  supply  of  that 
gas. 

Since  the  slow  combustion  within  the  body  sets  free  the 
same  amount  of  energy  as  does  the  rapid  combustion  of 
the  same  substances,  by  burning  a  quantity  of  food  equal 
to  that  which  a  man  eats  in  a  day  and  measuring  the  heat 
given  off,  the  amount  of  energy  which  that  food  can  sup- 
ply may  be  estimated.     In  that  way  it  has  been  shown 


208 


UNCONSCIOUS  NERVOUS   OPERATIONS 


that  the  energy  from  the  fats  is  about  equal  to  that  from 
proteids  and  carbohydrates  together.  It  has  been  esti- 
mated by  a  high  authority  that  a  healthful  diet  contains 
from  three  and  a  half  to  four  and  a  half  times  as  much  of 
nonnitrogenous  as  of  the  nitrogenous  foods. 

297.  The  following  table,  from  Landois  and  Stirling's 
Physiology,  gives  approximately  the  relative  amounts  of 
nitrogenous  and  nonnitrogenous  elements  in  common 
articles  of  food,  and  shows  that,  next  to  human  milk, 
wheat  flour  has  most  nearly  the  right  proportion  of  the 
two  elements.  Beef  and  other  kinds  of  flesh  have  too 
much  proteid  and  should  be  eaten  with  potatoes  or  rice, 
which  supply  the  nonnitrogenous  matter  needed  to  make 
the  food  complete.  Vegetables  contain  too  little  nitro- 
gen to  be  used  alone  as  food. 


Nitrogenous    Nonnitrogenous 


Veal       . 
Rabbit's  flesh 
Beef       . 
Beans    . 
Peas 
Mutton 
Pork      . 
Cow's  milk 
Human  milk 
Wheat  flour 
Oatmeal 
Rye  meal 
Barley   . 
Potatoes 
Rice 
Buckwheat 


298.  Variation  in  the  Amount  of  Food  Required.  —  When 
the  body  is  at  rest  the  amount  of  waste  is  much  less  than 
it  is  when  the  muscles  are  engaged  in  active  labor.     Then 


10 

to 

1 

10 

to 

2 

ro 

to 

17 

10 

to 

22 

10 

to 

23 

10 

to 

27 

10 

to 

30 

10 

to 

30 

10 

to 

37 

10 

to 

46 

10 

to 

50 

10 

to 

57 

10 

to 

57 

10 

to 

115 

10 

to 

123 

10 

to 

130 

FOOD  209 

the  muscular  tissue  is  rapidly  broken  down  under  the 
strong  contraction  constantly  called  for,  and  the  circula- 
tion becomes  swifter  to  supply  material  to  rebuild  the 
decomposed  cells.  Respiration,  too,  must  be  quickened 
to  furnish  a  sufficient  quantity  of  oxygen  to  arterialize 
the  blood  flowing  faster  to  the  lungs,  loaded  with  the 
products  of  chemical  changes  in  the  tissue  cells.  Nerv- 
ous tissue  also  is  worn  away  by  the  constant  demands 
upon  it  for  conveying  impulses  to  the  many  muscles 
engaged  and  in  coordinating  all  their  related  actions. 

If  the  body  is  exposed  to  a  low  temperature,  a  still 
larger  demand  is  made  for  food  to  supply  the  greater  loss 
of  heat.  During  the  period  of  growth  a  quantity  of  food 
is  needed  in  excess  of  the  waste  products  to  furnish  mate- 
rial for  enlarging  and  strengthening  all  parts  of  the 
body. 

299.  Undigested  Food.  —  Some  (an  average  of  about  one 
tenth)  of  the  food  taken  into  the  stomach,  and  especially 
a  part  of  our  vegetable  food,  seems  to  play  no  part  in  sup- 
plying nutrient  material,  but  passes  through  the  alimen- 
tary canal  to  be  expelled  from  the  body  unchanged.  It 
serves,  however,  as  an  aid  to  digestion  by  giving  an 
increase  of  bulk  to  the  food,  and  so  assists  the  action  of 
the  digestive  organs. 

300.  Cooking  is  the  application  of  heat  in  one  way  or 
another  to  articles  used  as  food.  Most  of  our  diet  comes 
to  the  table  after  being  submitted  to  this  process,  which 
renders  it  more  wholesome  and  more  palatable.  By  cook- 
ing, which  lessens  the  cohesion  of  particles,  the  amount 
of  work  required  of  the  digestive  organs  is  reduced,  and 
the  chemical  effects  of  heat  prepare  the  various  elements 
in  the  food  to  receive  more  readily  the  action  of  the  diges- 
tive juices.     Cooking  also  develops,  especially  in  animal 


210  rxcoxscious  xertous  operations 

foods,  the  agreeable  flavors  which  stimulate  not  only  the 
appetite,  but  also  the  secretion  of  the  digestive  juices. 

Another  very  important  effect  of  the  application  of 
heat  in  the  cooking  of  food  is  the  destruction  of  many  of 
the  germs  of  disease  which  are  sometimes  introduced  into 
the  human  system  with  food.  Certain  diseases  of  animals 
whose  flesh  is  eaten  by  man  may  thus  }je  communicated 
to  him  if  the  meat  is  not  first  thoroughl}-  cooked.  Dis- 
ease is  often  conveyed  also  by  means  of  the  water  supplied 
to  a  town  or  a  dwelling,  and  in  all  cases  where  there  is 
reason  for  suspicion  respecting  the  purity  of  the  water 
used  for  drinking,  it  should  be  boiled  for  at  least  half  an 
hour  before  using.  Tliis  sterilizes  it.  Ice  should  never 
be  mixed  with  drinking  water,  on  account  of  its  impuri- 
ties. Sterilized  water  may  be  cooled  for  drinking  pur- 
poses by  inclosing  it  in  tight  cans  of  glass  or  metal  and 
placing  the  cans  in  contact  with  the  ice. 

Much  of  our  food  comes  to  the  table  badly  prepared, 
cooked  too  much  or  too  little,  or  in  an  unhealthful  man- 
ner. The  importance  of  good  cooking  cannot  be  overesti- 
mated; the  lack  of  it  is  a  fruitful  source  of  the  widely 
prevalent  disease,  dyspepsia,  from  which  result  innumer- 
able physical  and  mental  ills.  In  recent  years  much 
attention  has  been  paid  to  scientific  cookery,  and  it  is 
now  taught  in  many  schools.  Only  a  few  hints  can  be 
given  here. 

301.  Cooking  of  Meats.  —  Fresh  meat  which  is  to  be  boiled 
should  be  put  at  first  into  water  which  is  already  boiling 
briskly.  After  fifteen  minutes  the  kettle  should  be  placed 
where,  for  the  rest  of  the  time,  the  water  Tsdll  only  bubble 
slightly.  By  applying  strong  heat  at  first,  the  albumin 
of  the  surface  of  the  meat  is  hardened  and  forms  a  close 
coating  which  retains  the  nutritive  juices  within. 


FOOD  211 

When  soup  or  broth  is  to  be  made,  this  process  is 
reversed  —  the  object  being  to  extract  the  soluble  portion 
of  the  meat  from  the  fiber.  The  meat  is  cut  into  small 
pieces  and  the  bones  are  cracked.  All  is  then  placed  in 
cold  water  without  salt,  and  heated  slowly  to  a  tempera- 
ture just  below  the  boiling  point.  It  should  be  kept  as 
hot  as  possible,  without  actually  boiling,  for  from  six  to 
eight  hours. 

Salt  meat  may  be  placed  in  cold  water  and  gradually 
heated.  Corned  beef  requires  boiling  for  about  five 
hours. 

Roasting  and  hahing  are  done  before  an  open  fire  or  in 
an  oven.  The  meat  should  first  be  browned  by  exposure 
to  a  very  high  temperature,  in  order  to  preserve  the  juices, 
and  the  heat  should  then  be  reduced. 

In  broiling  and  frying  the  same  principle  applies. 
Frying  is  regarded  as  the  least  healthful  of  the  various 
ways  of  preparing  food,  because  the  fat  which  coats  the 
surface  is  supposed  to  be  indigestible.  Anything  cooked 
by  frying  should  be  quickly  and  wholly  immersed  in  fat 
so  hot  that  the  surface  browns  at  once  and  further 
absorption  of  fat  is  prevented.  Then  the  heat  should  be 
lowered. 

By  stewing  and  braising,  meats  may  be  economically 
cooked  at  a  moderate  temperature,  but  the  process  re- 
quires several  hours.  In  stewing,  the  temperature  should 
not  quite  reach  the  boiling  point.  In  braising,  which  is 
done  in  a  closely  covered  pan  in  an  oven,  a  higher  degree 
of  heat  is  applied.  By  these  two  methods  the  tougher 
and  cheaper  cuts  of  meat  may  be  made  entirely  tender, 
nutritious,  and  appetizing. 

302.  Fish.  —  Principles  similar  to  those  suggested  above 
apply  to  the  cooking  of  fish. 


212  UNCONSCIOUS  NERVOUS   OPERATIONS 

303.  Eggs.  —  Eggs  are  made  most  digestible  by  placing 
them  (in  their  shells)  in  cool  water,  applying  heat,  and 
removing  them  from  the  water  as  soon  as  it  boils.  Or, 
they  may  be  put  into  water  already  boiling,  the  vessel 
being  covered  and  at  once  removed  to  where  the  water 
will  keep  warm  but  will  not  boil.  They  will  be  "  done  " 
in  from  ten  to  fifteen  minutes,  according  to  the  weather 
and  the  amount  of  water  used.  In  eggs  cooked  in  this 
way,  the  albumen,  which  by  boiling  becomes  hard  and 
difficult  of  digestion,  remains  soft,  creamy,  and  nutritious, 
while  the  yolk  is  partly  solidified  and  rendered  more 
palatable. 

304.  Cooking  of  Vegetables.  —  Fresh  vegetables  should  be 
placed  in  boiling  water  only  long  enough  to  soften  the 
fiber  and  cause  the  starch  granules  to  burst.  Too  much 
cooking  injures  them. 

Dried  seeds  require  longer  boiling,  and  it  is  often  well 
to  soak  them  in  water  for  several  hours  before  cooking. 

305.  Bread  is  our  most  valuable  food.  It  is  made  from 
the  various  grains,  also  from  the  flour  of  certain  nuts 
and  rootstocks.  Salt,  water,  and  yeast,  in  proper  propor- 
tions, and  sometimes  a  small  quantity  of  sugar  to  hasten 
fermentation,  are  added  to  the  flour  or  meal,  and  the  mass 
is  allowed  to  become  ''  light "  by  the  fermentation  of  the 
yeast  before  baking.  Numerous  chemical  changes  take 
place  in  the  jDrocess.  The  water  dissolves  the  gluten  and 
sugar  of  the  flour  and  swells  the  starch  granules.  If  the 
dough  is  at  a  temperature  of  100°  F.,  fermentation  at 
once  sets  in ;  some  of  the  starch  becomes  sugar ;  sugar  is 
converted  into  alcohol  and  carbonic  acid ;  the  gas  formed 
expands  in  little  bubbles,  which  are  surrounded  by  walls 
of  sticky  gluten,  and  "raises"  the  bread.  If  the  fer- 
mentation is  allowed  to  continue  too  long,  a  new  chemical 


FOOD  213 

product,  called  acetic  acid,  appears,  rendering  the  bread 
sour  and  unwholesome. 

A  few  things  are  indispensable  to  the  making  of  good 
bread.  A  good  quality  of  flour  must  be  used  and  good 
yeast  (Miss  Parloa  considers  the  ''  compressed  yeast " 
sold  in  the  shops  and  bakeries  the  best  procurable).  The 
dough  should  have  at  first  a  temperature  of  100°  F., 
which  should  later  be  reduced  to  70°.  The  mass  must 
be  kneaded  sufficiently  to  distribute  the  yeast  evenly 
throughout,  and  again  after  it  has  "  risen  "  to  break  the 
bubbles  of  gas  and  force  it  to  permeate  every  part,  that 
the  loaf  may  be  rendered  light  and  spongy  by  innumera- 
ble fine  pores.  After  the  final  kneading  and  shaping  into 
loaves,  they  should  be  left  to  rise  to  about  twice  their 
original  size  before  baking.  The  oven  should  be  heated 
to  about  400°,  but  for  the  last  half  of  the  baking  the 
temperature  should  be  reduced  to  300°.  In  baking,  the 
process  of  fermentation  is  checked  as  soon  as  the  loaf  is 
raised  to  a  temperature  of  212°.  The  alcohol  is  vaporized 
and  driven  off,  the  starch  granules  burst,  and  by  the 
transformation  of  starch  into  sugar  and  dextrine  the 
delightful  sweetness  of  good  wheat  bread  is  developed. 
Very  large  loaves  are  undesirable,  as  acetic  acid  may 
be  formed  in  their  interior  after  they  are  placed  in  the 
oven.  Small  loaves  are  better  than  large  ones,  also 
because  they  have  a  larger  proportion  of  crust,  which  is 
the  sweetest  and  most  wholesome  part  of  the  loaf. 

Bread  made  of  whole-wheat  flour  is  especially  valuable 
for  children,  because  it  contains  more  of  the  elements 
which  are  needed  for  making  teeth  and  bone  than  does 
white  flour.  The  same  is  true  of  what  is  called  Graham 
flour,  but  the  coarse  bran  which  such  flour  contains  is  to 
some  persons  unwholesome. 


214  UNCONSCIOUS   NERVOUS   OPERATIONS 


Experiments 

Food  Elements.  —  Some  very  interesting  and  easily  performed 
experiments  may  be  made  upon  substances  common  in  ordinary  food. 

91.  Tests  for  Proteids.  —  To  one  fourth  of  a  test  tube  of  dilute  white 
of  egg  1  (a  proteid)  add  a  few  drops  of  strong  nitric  acid  and  boil. 
Cool  and  add  a  little  ammonia;  the  yellow  color  changes  to  orange. 
To  show  that  the  orange  color  is  due  to  the  presence  of  a  proteid, 
repeat  the  experiment,  using  pure  water  instead  of  white  of  egg. 
Another  test  is  as  follows :  To  one  fourth  of  a  test  tube  of  a  15  per 
cent  solution  of  caustic  soda  add  two  or  three  drops  of  a  1  per  cent 
solution  of  copper  sulphate.  Shake  the  mixture,  and  after  warming 
add  a  little  white  of  Qgg  or  other  solution  of  proteid ;  the  blue  color 
becomes  violet.  To  show  that  these  color  changes  are  tests  for  pro- 
teids, repeat  the.  above  experiments,  using  a  solution  of  sugar  and  the 
starch  solution  mentioned  below,  instead  of  the  white  of  egg. 

92.  Coagulation  of  Albumin  hy  Heat.  —  Boil  dilute  white  of  egg  in  a 
test  tube;  it  does  not  clot.  Then  add,  drop  by  drop,  dilute  acetic 
acid  (2  per  cent) ;  a  precipitate  of  coagulated  albumin  finally  sepa- 
rates. If  the  white  of  egg  is  not  diluted,  it  coagulates,  of  course,  on 
boiling. 

93.  Solubility  of  Starch.  —  Stir  some  starch  into  cold  water  and 
observe  that  it  does  not  dissolve.  Boil  the  mixture ;  solution  occurs, 
but  the  liquid  remains  somewhat  cloudy. 

94.  Test  for  Starch.  —  To  some  of  the  starch  solution  prepared 
above,  add  a  drop  of  iodine  solution.  The  blue  color  resulting  is  the 
characteristic  reaction  of  iodine  with  starch.  Dilute  the  starch  solu- 
tion and  repeat  the  experiment.  The  dilution  may  be  much  pro- 
longed before  the  blue  color  fails  to  appear  on  adding  iodine.  To 
show  that  the  blue  color  is  related  to  the  presence  of  starch,  add 
iodine  to  pure  water  or  any  liquid  from  which  starch  is  known  to  be 
absent. 

95.  Microscopical  Examination  of  Starch.  —  Scrape  the  fresh  cut  sur- 
face of  a  potato,  and  mount  in  water  on  a  slide  some  of  the  material 
thus  obtained.     Examine  with  the  compound  microscope.     Numerous 

1  To  prepare  dilute  white  of  egg,  beat  up  the  white  of  an  egg  with 
about  twenty  volumes  of  water,  filter  through  muslin,  and  pour  off 
gently  to  remove  air  bubbles  present. 


FOOD  215 

small  starcJi  granules  will  be  seen.  Each  granule  shows  concentric 
markings.  Add  iodine  solution  ;  the  granules  turn  blue  or  blue  black. 
Examine  other  kinds  of  starch  granules,  of  corn,  oats,  rice,  etc. 

96.  Test  for  Sugar.  —  To  one  fourth  test  tube  of  a  weak  solution 
of  glucose,  add  an  equal  amount  of  a  15  per  cent  solution  of  caustic 
soda.  Shake,  and  after  adding  a  few  drops  of  a  1  per  cent  solution 
of  copper  sulphate,  boil  for  a  few  minutes.  The  liquid  changes 
from  blue  to  yellow^,  or,  if  much  sugar  is  present,  to  brown  in  color, 
and  a  precipitate  is  formed.  To  show^  that  the  change  in  color  is  due 
to  the  sugar  present,  repeat  the  preceding,  using  pure  water,  or  any 
solution  known  not  to  contain  sugar,  instead  of  the  sugar  solution. 
This  test  is  known  as  Trommer's  test.  It  is  not  a  test  for  cane  sugar, 
nor  does  it  distinguish  between  glucose,  malt  sugar,  and  milk  sugar. 

97.  Fats.  —  Put  some  melted  batter,  qr  olive  oil,  into  a  test  tube 
one  fourth  full  of  water.  The  fat  rises  to  the  top.  Shake  well ;  a 
whitish  mixture,  or  emulsion,  is  the  result,  but  the  oil  and  water 
quickly  separate.  To  the  contents  of  the  test  tube,  add  an  equal 
amount  of  1  per  cent  solution  of  carbonate  of  soda  (an  alkali),  and 
shake.  The  emulsion  with  the  alkali  lasts  much  longer  than  that 
with  water  alone.  Add  a  drop  or  two  of  oleic  acid  (a  fatty  acid)  to 
the  mixture,  and  shake  well;  the  emulsion  lasts  longer  than  before. 
It  will  be  learned  later  that  the  fats  are  only  slightly  dissolved  in 
digestion,  but  are  chiefly  emulsified. 

98.  Examine  with  the  microscope  some  of  the  emulsion  prepared 
above.  The  fat  will  be  found  to  be  broken  up  into  innumerable  fine 
particles. 

99.  Shake  some  olive  oil  with  dilute  white  of  egg  in  a  test  tube ;  an 
emulsion  results. 

100.  To  one  fourth  test  tube  of  water,  add  a  few  drops  of  oleic 
acid,  and  shake.  The  oil  rises  to  the  surface  as  in  the  preceding- 
experiments.  To  the  contents  of  the  test  tube  add  carbonate  of  soda 
as  before.  A  white  precipitate  of  soap  is  formed.  An  alkali  and  a 
fatty  acid  form  soap. 

During  digestion  some  of  the  fat  is  broken  down  into  glycerin  and 
fatty  acids.  The  latter  unite  with  alkalis  in  the  intestine  to  form  sol- 
uble soap. 

101.  Flour.  —  Boil  a  little  flour  in  water  and  test  with  iodine  for 
starch. 

102.  Place  a  little  flour  in  from  five  to  ten  times  its  bulk  of  water 


216  UNCONSCIOUS  NERVOUS   OPERATIONS 

in  a  flask  and  allow  it  to  stand  several  hours,  shaking  it  occasion- 
ally. Filter  and  test  the  filtrate  for  proteids,  as  in  Ex.  91,  and  for 
sugar  as  in  Ex.  96. 

103.  Shake  some  flour  with  ether  in  a  test  tube  and  allow  it  to 
stand  for  an  hour  or  two,  keeping  the  tube  tightly  corked  and  shak- 
ing it  occasionally.  Filter  off  the  ether  and  place  some  of  it  on  a  clean 
glass  surface  and  allow  it  to  evaporate.  A  greasy  residue  remains, 
showing  that  the  flour  contained  fat,  some  of  which  was  dissolved  out 
by  the  ether. 

104.  Gluten.  —  Moisten  flour  with  water  till  it  forms  a  tenacious 
dough.  Tie  it  in  muslin  cloth  and  knead  it  in  a  vessel  of  water  till 
all  the  starch  is  separated.  There  remains  in  the  cloth  a  sticky,  elas- 
tic mass  of  gluten,  consisting  of  the  insoluble  albumins,  some  of  the 
ash,  and  the  fats.  Draw  out  some  of  the  gluten  into  threads,  and 
notice  its  tenacity. 

105.  Milk.  —  Examine  with  the  microscope  a  drop  of  fresh  milk. 
It  is  seen  to  be  an  emulsion  of  oil  globules  floating  in  a  liquid. 

106.  Warm  some  milk  in  a  flask,  and  add  a  few  drops  of  acetic 
acid.  The  mass  clots  and  separates  into  a  solid  curd,  consisting  of 
casein  and  fat,  and  a  liquid,  the  whey.  Caseinogen  is  the  chief  proteid 
of  milk.     In  curdling  it  is  changed  to  casein. 

107.  Dilute  milk  with  ten  times  its  volume  of  water  and  slowly  add 
dilute  acetic  acid.  As  long  as  the  liquid  remains  alkaline,  or  neutral, 
—  as  can  be  tested  with  litmus  paper,  —  no  visible  change  occurs,  but 
on  adding  more  and  more  of  the  acid  there  is  finally  formed  a  precipi- 
tate of  casein  which,  as  in  the  preceding  experiments,  carries  with  it 
most  of  the  fat. 

108.  Filter  the  curd  from  the  whey  obtained  in  one  of  the  preced- 
ing experiments,  and  test  the  filtrate  for  sugar  (milk  sugar)  and  pro- 
teids  (see  Exs.  96  and  91) . 

109.  Test,  with  litmus  paper,  some  perfectly  fresh  milk.  It  will 
be  found  to  be  neutral,  or  alkaline.  Allow  it  to  stand  in  a  warm  place 
till  it  becomes  sour  and  curdles.  It  will  be  found  to  be  acid  in  reac- 
tion. In  the  souring  of  milk  the  milk  sugar  changes  to  lactic  acid, 
and  curdling  is  finally  produced  by  the  acid,  as  was  illustrated  in 
preceding  experiments. 

110.  Lean  Meat.  —  Mince  finely  some  perfectly  fresh  muscles  of  a 
cat,  dog,  or  rabbit.  Place  them  in  a  large  jar  of  water  and  stir.  In 
about  a  quarter  of  an  hour  filter  through  muslin  and  place  the  muscle 


FOOD  217 

in  a  fresh  jar  of  water.  Test  the  filtrate  for  proteids  (serum  albumin) 
as  in  Ex.  91.  Repeat  the  washing  till  the  filtrate  gives  no  test  of  pro- 
teids. An  hour  or  two  of  washing  will  suffice.  Then  squeeze  out  the 
water  from  the  minced  muscle,  grind  up  the  latter  with  clean  sand, 
and  add  ten  times  its  volume  of  a  10  per  cent  solution  of  common 
salt.  Stir  occasionally,  and  after  an  hour  or  more  filter  through  mus- 
lin. Add  some  of  the  filtrate,  drop  by  drop,  to  a  large  vessel  of  pure 
water ;  there  is  formed  a  milky  precipitate  of  myosin,  the  chief  proteid 
of  muscle.  In  the  living  muscle  the  myosin  exists  as  the  soluble 
myosinogen.  Thus  in  muscle  there  are  seen  to  be  two  kinds  of  pro- 
teids :  one,  serum  albumin,  soluble  in  water,  the  other,  myosin,  in- 
soluble in  water,  but  soluble  in  weak  salt  solution. 


CHAPTER   XVII 

THE  DIGESTIVE  APPARATUS  AND   NUTRITION 

306.  The  apparatus  for  digestion  consists  of  the  alimen- 
tary canal  with  its  appendages.  This  is  a  long,  irregular 
tube  having  a  continuous  lining  of  mucous  membrane. 
It  comprises  the  mouthy  pharynx^  esophagus^  stomachy  and 
large  and  small  intestines.  Numerous  glands  along  its 
length  furnish  the  digestive  juices.^ 

307.  The  Mouth  (Fig.  108)  is  the  chamber  which  re- 
ceives the  food  through  the  opening  and  closing  lips. 
The  soft  palate  at  the  back  forms  a  curtain  over  the 
opening  at  the  back,  while  the  hard  palate  of  the  roof, 
the  soft  muscular  Avails  of  the  cheeks^  and  the  large  muscle 
of  the  tongue^  together  with  the  teeth.,  all  assist  in  the 
process  of  mastication  to  which  the  food  is  first  subjected. 
As  in  the  skin,  many  minute  papillce  are  found  in  the 
mucous  membrane,  containing  networks  of  nerves  and 
blood  vessels.  Some  of  these  contain  taste  corpuscles. 
Some  have  organs  for  touch. 

308.  The  Teeth  are  the  special  organs  for  cutting  and 
grinding  the  food.  Two  sets  of  teeth  are  provided. 
The  first,  which  appear  in  infancy  and  are  only  twenty 
in  number,  are  called  temporary  or  milk  teeth.  They  fall 
out  after  a  few  years,  to  be  replaced  by  the  permanent 
teeth.,  thirty-two  in  number. 

The  four  front  teeth  on  each  jaw  are   called  incisors. 

218 


THE    DIGESTIVE   APPARATUS    AND    NUTRITION        219 


Next  to  them  come  the  cafmies^  one  on  each  side,  then  the 
two  bicuspids,  or  premolars,  and  next  to  them  three  molars 
on  each  side.  The  tliird  pair  of  molars  on  each  jaw  are 
called  the  wisdom  teeth,  and  they  sometimes  fail  to  appear. 


Opening  of 
J]iistachian  tube 


Soft  palate 


Larynx 


Hard  i)alate 


Tongue 


Hyoid  bone 
- —  False  vocal  cords 
— '  True  vocal  cords 

Thyroid  carti- 
lage 

^^^  Cricoid  carti- 
lage 


Fig.  108.  —Vertical  section  of  the  head  and  neck. 

The  teeth  of  different  animals  are  adapted  in  form  and 
structure  to  the  food  upon  which  they  subsist.  Carnivo- 
rous animals  are  provided  with  strong,  sharp  teeth  for 
seizing  and  tearing  flesh,  while  the  teeth  of  herbivorous 
animals  are  broader  and  relatively  shorter,  with  wide- 
ridged  surfaces  for  grinding  grains  and  plant  fiber.  Man, 
as  requiring  both  animal  and  vegetable  food,  is  provided 
with  teeth  of  both  sorts. 

309.  Structure  of  a  Tooth  (Fig.  109). — A  tooth  has  three 
parts, —  crown,  neck,  emdroots.  The  crown  is  the  part  which 
projects  beyond  the  gum,  and  is  covered  with  the  firm. 


220 


UNCONSCIOUS   NERVOUS   OPERATIONS 


solid  layer  of  enamel^  the  hardest  tissue  found  in  the  body. 

The  nech  is  the  narrowed  portion  just  below  the  crown, 

surrounded  by  the  gum.  The 
root  (one  or  more)  is  the  re- 
mainder of  the  tooth,  which  is 
secured  to  the  socket  of  the 
jaw  by  means  of  the  perios- 
teum, through  which  it  derives 
nourishment.  A  tooth  is  com- 
posed of  a  hard,  close  material 
called  dentine^  much  like  bone, 
but  with  less  animal  matter. 
This  is  -molded  round  the  cen- 
tral pulp  cavity^  which  contains 
the  tooth  pulp  —  a  mass  of  loose 
connective  tissue,  blood  vessels, 
nerves,  and  cells  of  different 
shapes,  one  sort  of  which  builds 
the  dentine.  A  layer  of  true 
bone,  called  tooth  cement,  sur- 
rounds the  dentine  of  that  part 
of  a  tooth  embedded  in  the  gum, 
as  enamel  caps  the  crown. 

310.  The  Tonsils.  —  Between  the  arches  of  the  soft  palate 
lies  on  each  side  a  soft  rounded  body  covered  with  mucous 
membrane  and  containing  many  small  glands  which  se- 
crete mucus.  They  are  called  the  tonsils  (Fig.  108). 
Their  use  is  unknown  except  that  they  furnish  some  pro- 
tection to  the  larynx  and  pharynx.  Being  sometimes 
permanently  enlarged  and  subject  to  frequent  inflamma- 
tion, they  are  occasionally  removed  by  the  surgeon  with 
apparent  advantage  to  the  patient. 

311.  The  Pharynx  (Fig.  108)  lies  behind  the  soft  palate. 


Cement 


Fig.  109.  — Diagram  of  the 
structure  of  a  tooth. 


THE   DIGESTIVE   APPARATUS   AND   NUTRITION       221 

It  has  muscular  walls,  mostly  of  voluntary  fibers,  which 
contract  upon  the  food  to  push  it  into  the  esophagus,  or 
may  force  it  back  into  the  mouth  if  desired.  Seven 
passages  open  into  this  cavity:  the  mouthy  the  two  nasal 
passages^  the  two  Eustachian  tubes,  tlie  larynx,  and  the 
esophagus. 

312.  The  Esophagus  connects  the  pharynx  with  the  stom- 
ach (Figs.  108  and  110).  It  is  a  muscular  tube  lying 
along  the  spinal  column  behind  the  trachea.  The  muscu- 
lar coat  of  the  wall  of  the  esophagus  contains  an  external 
layer  of  fibers  running  lengthwise,  while  the  second  layer 
is  of  circular  fibers.  They  are  mainly  involuntary  and 
supplied  by  the  vagus  nerve,  with  fibers  from  sympathetic 
ganglia  also. 

313.  The  Stomach  lies  in  the  cavity  of  the  abdomen 
immediately  below  the  diaphragm  (Fig.  86,  p.  153). 
It  is  a  large  sac,  formed  by  the  dilation  of  the  alimentary 
canal  (Fig.  110),  and  its  walls  have  the  three  coats  of 
the  rest  of  that  canal,  —  the  inner  mucous  coat,  the  middle 
connective  tissue  coat,  and  the  external  muscular  coat,  with 
a  fourth  coat  in  addition,  the  p^^f^ioneum,  which  forms  the 
lining  of  the  abdominal  cavity  and  is  reflected  back  over 
the  organs  (or  most  of  them)  which  it  contains.  The 
peritoneum  adheres  to  the  walls  of  the  abdominal  cavity, 
folds  of  it  surround  the  blood  vessels  running  to  the 
stomach,  and  a  large  pouch  of  the  same  forms  a  sling  for 
the  stomach.  From  the  lower  side  of  the  stomach  another 
large  fold  of  the  peritoneum,  called  the  great  omentum, 
spreads  OA^er  the  rest  of  the  abdomen.  After  middle  life 
it  often  holds  a  large  accumulation  of  fat. 

The  muscular  coat  of  the  stomach  is  composed  of  layers 
of  unstriped  muscular  fibers.  Its  mucous  lining  is  inelas- 
tic, and  as  it  lines  the  organ  smoothly  when  it  is  distended, 

macy's  phys.  — 14; 


222  UNCONSCIOUS   NERVOUS   OPERATIONS 

it  must  lie  in  folds  when  the  stomach  is  empty  and 
shrunken  (Fig.  110).  The  blood  supply  of  this  mem- 
brane is  very  large  during  digestion,  and  its  appearance 
is  then  much  redder  than  at  other  times.     The  two  ox^en- 


Fig.  110.  — stomach  and  duodenum. 

The  anterior  walls  are  cut  away  to  show  the  folds  of  the  mucous  membrane, 
rugse  of  stomach,  and  valvulai  conniventes  of  intestine. 

ings  of  the  stomach  are  both  upon  the  upper  side.  That 
near  the  left  end,  the  cardiac  orifice^  admits  the  food  from 
the  esophagus;  that  on  the  right,  t\iQ  pyloric  orifice,  con- 
nects with  the  small  intestine.     The  latter  is  surrounded 


thp:  digestive  appakatt^s  and  NrxRiTiox     228 

by  a  thick  ring  of  circular  muscular  filler,  forming  a 
sphincter  muscle,  which  keeps  the  opening  closed  except 
when  food  is  ready  to  pass  from  tlie  stomach. 

314.  Nervous  Supply  of  the  Stomach.  —  Nerve  fibers  from 
many  centers  reach  the  different  coats,  glands,  and  blood 
vessels  of  the  stomach  and  those  of  the  large  and  small 
intestines.  They  are  gathered  in  large  tangles  of  nervous 
matter,  called  plexuses,  which  contain  Ijranches  from  the 
vagus  nerves,  from  many  of  the  spinal  nerves,  and  from 
the  ganglia  of  the  sympathetic  chain.  The  great  solar 
plexus,  or  epigastric  i^lexus,  is  2>h^<^ed  at  the  pit  of  the 
stomach  (Fig.  22,  p.  31);  the  hypogastric  plexus  lies 
before  the  last  of  the  lumbar  vertebrae,  and  divides  into 
two  parts,  one  lying  on  each  side  of  the  rectum.  These 
plexuses  give  rise  to  innumerable  branches  which  control 
the  complicated  processes  of  digestion,  the  precise  path  of 
each  different  sort  of  nervous  influence  not  having  been 
yet  made  out.  It  is  easy  to  see,  however,  that  this  close 
nervous  connection  of  the  digestive  organs  with  all  parts 
of  the  system  implies  important  relations  between  them. 

Vagus  nerve  fibers  appear  to  stimulate  the  peristaltic 
or  wavelike  movement  of  the  stomach  and  bowels,  which 
by  the  progressive  narrowing  of  the  tube  forces  on  its 
contents,  wdiile  the  sympathetic  fibers  are  inhibitory  and 
bring  the  movements  to  an  end.  It  is  believed  that  the 
walls  of  these  organs  possess  some  power  of  spontaneous 
action  such  as  appears  in  the  Avails  of  the  heart. 

315.  The  Small  Intestine  (  Fig.  Ill )  is  a  tube  with  many 
curves,  about  twenty  feet  in  length,  two  inches  in  diameter 
at  its  upper  end  and  somewhat  smaller  in  its  loAver  por- 
tion. Its  coats  are  the  same  as  those  of  the  stomach,  but 
the  peritoneum,  a  fold  of  whicli  forms  the  outer  coat,  does 
not  entirely  surround  the  tube,  but  runs  off'  to  form  a  sup- 


224 


UNCONSCIOUS   NERVOUS   OPERATIONS 


porting  membrane  for  the  intestine,  called  the  mesentery. 

This  is  gathered  up  and  connected  with  the  wall  of  the 

abdominal  cavity  near  the  spinal 
column.  The  blood  vessels  and 
nerves  pass  through  the  mesen- 
tery to  reach  the  intestine,  and 
the  absorbents  also  pass  through 
it  from  the  intestine.  The  two 
layers  of  muscular  fibers,  one 
circular  and  one  longitudinal, 
in  the  intestinal  wall,  are  of  the 
unstriped,  involuntary  kind. 

316.  Nerves  of  the  Small  Intes- 
tine. —  Between  the  muscular 
layers  is  a  plexus  of  nerve  fibers 
with  many  ganglia,  and  in  the 
layer  beneath  the  mucous  mem- 
brane of  the  lining  is  another 
nerve  plexus,  also  gangliated. 

317.  The  Mucous  Membrane  of 
the  Small  Intestine  has  a  very 
important  part  in  the  function 
of  digestion,  and  is  of  peculiar 
structure.  Like  the  lining  mem- 
brane of  the  stomach,  it  has  an 
inner  layer  of  columnar  epithe- 
lium, but  unlike  that  of  the 
stomach  the  lining  of  the  intes- 
tine is  for  a  large  part  of  its 
length  laid  in  folds  which  do 
not  disappear  when  the  canal  is 

are    called  valvuloe    conniventes 
(Fig.   110).      The}^  lie  around   the  inner  surface  of  the 


and 


13 

Fig .   Ill—  The    stomach 
intestines. 

1  stomach. 

2  duodenum. 

3  small  intestine. 

4  termination  of  the  ileum. 
.5  caecum. 

6  vermiform  appendix. 

7  ascending  colon. 

8  transverse  colon. 

9  descending  colon. 

10  sigmoid  flexure  of  the  colon. 

11  rectum. 

12  spleen. 
1.3  anus. 

distended.       These    folds 


THE    DIGESTIVE    APPARATUS   AND   NUTRITION       225 


intestine,  each  separate  valviila  reaching  about  one  half 
or  t^yo  thirds  the  way  round.  Their  function  is  to  fur- 
nish a  Lirge  amount  of  secreting  and  absorbing  surface. 

318.  The  Villi. — Still  further  to  increase  this  surface, 
the  Yalvula3  are  covered  with  villi.  These  are  minute 
projections  from   one  fiftieth   to    one   eighth  of   an   inch 


Fig.  112. 


Diagrammatic  representation  of  a  small  area  of  the  mucous 
membrane  of  the  small  intestine. 


1  celliilar  structure  of  the  epithelium, 

or  outer  layer. 

2  a  vein. 

3  fibrous  layer. 

•4  Tilli  covered  -with  epithelium. 

5  a  villus  in  section,  showing  its 
covering  of  epithelium,  and  its 
blood  vessels  and  lymphatics. 


6  a  villus  partly  uncovered. 

7  a  villus  stripped  of  its  epithelium. 

8  lymphatics  or  lacteals. 

9  orifices  of  the  glands  opening  be- 

tween the  villi. 
10,  11,  12  glands. 
13  capillaries  surrounding  the  orifice 

of  a  srland. 


in  length,  and  are  found  only  in  the  small  intestine  (Fig. 
112).  They  give  to  its  mucous  lining  a  peculiar  velvety 
appearance.  Each  villus  is  covered  with  columnar  epithe- 
lium restino-  on  a  fine  membrane.    Within  are  blood  vessels 


226 


UNCONSCIOUS   NERVOUS   OPERATION'S 


(two  or  more  arteries,  a  dense  network  of  capillaries,  and 
one  or  tw^o  veins),  connective  tissue  fibers,  and  a  single 

lymphatic  or  lacteal  ves- 
sel, which  may  be  looped 
or  branched  (Fig.  113). 
Between  blood  vessels 
and  lymphatics  is  a  very 
thin  layer  of  fine  muscu- 
lar fibers,  which  help  to 
propel  the  chyle  along 
the  lacteals.  Fine  nerve 
fibers  are  also  found.  In 
the  villi  the  digested 
food  passes  through  the 
cells  of  the  thin  wall 
into  blood  vessels  and 
lacteals. 

319.  The  Large  Intestine 
(Fig.  111).— The  small 
intestine  passes  into  the 
large  intestine^  the  ileo- 
coeeal  valve  at  the  junc- 


Fig.  113.  — Diagram  of  the  essential 
parts  of  a  villus. 

a  epithelium    which    takes    up    food  and     tion   preventing   any  re- 
transports  it  to  the  tubes  within. 
6  an  artery,      c  capillaries,      d  a  lacteal 


flux  of  the  contents  from 
the  large  to  the  small 
tube.  The  large  intestine  has  three  parts,  called  the 
ccecum,  the  eolon^  and  the  rectum.  The  ccecura  is  a  large 
sac  on  the  right  side,  which  receives  the  contents  of 
the  small  intestine.  Attached  to  the  lower  side  of  the 
caecum  is  the  small  vermiform  appendix^  which  has  no 
known  function,  but  is  regarded  as  a  "  survival "  from 
a  previous  type  of  animal  structure.  Continuous  with 
the  ciecum  is  the  colon,  having  ascending,  transverse,  and 


THE   DIGESTIVE   APPAHATUS   AND   NUTRITION       227 


descending  parts.  The  rectum  is  the  final  portion  of  the 
alimentary  canal ;   it  opens  externally  at  the  aiius. 

The  walls  of  the  large  intestine  are  like  those  of  the 
small  intestine,  except  that  the  valvulse  conniventes  and  the 
villi  are  wanting.  In  the  caecum  and  colon  the  longitudi- 
nal muscular  fibers  are  for  the  most  part  collected  in  three 
bands,  which,  being  shorter,  from  end  to  end,  than  the  other 
coats,  draw  up  the  intestinal  Avail  into  puckers,  or  folds. 

The  muscular  coat  of  the  rectum  is  much  thicker  than 
elscAvhere,  and  at  the  anus  is  a  strong  band  called  the 
internal  sphincter  muscle. 

320.  Secretion.  —  All  the  living  cells  of  the  body  are 
engaged  in  taking  from  the  blood  certain  substances  suit- 
able for  their  own  special  purposes,  and  returning  to  the 
blood  those  particles  of  matter  which  have  fulfilled  their 
mission  and  are  no  longer  of  use.  Every  cell  requires 
oxygen,  and  oxidation  is  now 
understood  to  occur  within 
all  the  cells.  But  certain 
cells  or  groups  of  cells  take 
up  also  other  substances  from 
the  blood,  and  manufacture 
within  themselves  a  new 
product  having  a  special 
function.  This  process  is 
called  secretion^  and  the  or- 
gans of  secretion  are  called 
glands. 

321.  Glands.  —  The    sim- 
plest    glands     are     merely 
minute  tubes  lined  with  cu- 
bical cells  (Fig.  114).     Sometimes  these  tubes  branch  at 
the  inner  end,  all  the  branches  being  lined  with  the  secret- 


Fig.  114.  — structure  of  glLi.cc. 

1  simple  pit,  surrounded  by  capillaiics. 

2  flask-shaped  gland,  with  short  duct. 
3,  4  more  complex  glands,  with  longer 

ducts. 


228  UNCONSCIOUS  NERVOUS   OPERATIONS 

ing  cells,  and  all  uniting  in  a  single  tube,  or  duct^  through 
which  the  secretions  pass.  Frequently  a  large  number  of 
branches  from  a  secreting  tube  are  grouped  together  in 
clusters  to  form  an  organ  of  considerable  size,  as  the  liver 
or  the  pancreas. 

The  secreting  surface  is  always  composed  of  living 
cells,  and  the  processes  carried  on  in  them  are  similar  to 
those  occurring  in  other  cells.  That  is,  secretion  involves 
building  up,  or  growth,  and  breaking  down,  or  waste,  of 
the  cell  substance,  along  with  other  changes.  Under  the 
microscope  the  cells  of  the  glands  are  seen  to  contain  a 
nucleus  and  many  granules.  These  granules  are  products 
of  the  cell  itself.  When  the  secreting  process  is  going  on, 
water  and  other  substances  pass  through  the  cells  from 
the  blood,  and  at  the  same  time  the  granules  are  dissolved 
in  the  water  and  pass  out  along  the  secretory  duct.  Secre- 
tion is  a  manufacturing  process,  and  not  merely  a  filter- 
ing out  of  certain  substances  from  the  blood.  In  each 
gland  the  chief  or  specific  constituents  of  its  peculiar  juice 
are  formed  in  the  cell  and  not  simply  extracted  from  the 
blood. 

The  mucous  membrane  of  the  whole  of  the  alimentary 
canal  is  largely  made  up  of  glands. 

322.  Salivary  Glands  (Fig.  115). — There  are  three  pairs 
of  salivary  glands.  Those  lying  in  front  of  each  ear  are 
the  parotid  glands;  those  under  the  lower  jaw  on  each 
side,  the  submaxillary  glands;  and  those  under  the  tongue, 
the  sublingual  glands.  They  are  large  glands  whose  ducts 
pour  their  watery  secretions  into  the  mouth. 

323.  Nervous  Action  upon  the  Salivary  Glands.  —  Ordina- 
rily the  nervous  action  affecting  the  salivary  glands  is 
reflex.  The  organs  of  taste  are  stimulated  by  food,  or 
the  sight  or  odor  of  food  stimulates  the  optic  or  olfactory 


THE   DIGESTIVE   APPAUATUS   AND   NUTRITION       229 


nerves,  the  nervous  center  in  the  bi'ain  sends  impulses  to 
the  special  center  in  the  medulla  oblongata  from  which 
efferent  secretory  im- 
pulses are  reflected, 
and  they  pass  along 
the  fibers  of  a  branch 
of  the  seventh  cranial 
nerve,  which  probably 
contains  fibers  from 
the  ninth  nerve,  with 
which  it  communi- 
cates. The  impulse 
finally  reaches  the 
cells  of  the  submaxil- 
lary and  sublingual 
glands,  and  a  flow  of 
saliva  results.  Even 
the   thought  of  food, 


Fig  115. 


The  salivary  glands  of  the 
right  side. 


by  stimulating  a  center  in  the  brain,  may  produce  nervous 
impulses  having  the  same  effect.  Nerve  branches  from 
the  sympathetic  system  also  carry  stimulus  to  these 
glands. 

For  the  parotid  glands  the  chief  secretory  nerve  fibers 
arise  in  the  glossopharyngeal  nerves  (ninth  cranial). 

324.  Action  of  Saliva.  —  A  part  of  the  digestion  of  food 
takes  place  in  the  mouth.  Saliva  is  mixed  with  the  food 
by  mastication,  and  serves  to  moisten  the  mass  and  lubri- 
cate it  for  swallowing.  It  also  causes  a  chemical  action, 
due  to  the  presence  of  its  active  principle,  ptyalin^  which 
affects  the  starch  in  food,  converting  it  into  malt  sugar. 
If  one  chews  slowly  a  few  grains  of  Avheat,  he  will  notice 
that  the  paste  becomes  sweet.  This  is  because  some  of  the 
starch  in  the  wheat  is  changed  by  the  saliva  into  sugar. 


230  UNCONSCIOUS   NERVOUS   OPERATIONS 

325.  Ferments.  —  The  ptyalin  belongs  to  a  kind  of  sub- 
stances called  fer7ne7its.  Of  these  there  are  two  classes, 
—  the  organized  and  the  unorganized.  The  organized 
ferments  are  living  vegetable  organisms.  Yeast  is  one 
of  them,  the  vinegar  |??a7i^  is  another,  and  the  various 
kinds  of  bacteria^  some  of  which  cause  disease,  are  other 
examples.  The  unorganized  ferments  are  chemical  sub- 
stances resulting  from  the  activity  of  living  cells,  and 
capable  of  effecting  certain  changes  in  particular  sub- 
stances. The  ptyalin  is  one  of  these.  The  ferments  are 
the  agents  for  effecting  most  of  the  changes  which  the 
food  undergoes  in  digestion. 

326.  Gastric  Juice.  —  The  epithelium  of  the  lining  of  the 
stomacli  consists  of  a  single  layer  of  cells,  and  the  mucous 
membrane  is  almost  entirely  composed  of  simple  tubelike 
glands  closely  packed  together.  When  food  reaches  the 
stomach,  more  blood  is  sent  into  the  dilated  blood  vessels, 
and  the  glands  make  from  the  bhjod  a  colorless  fluid  called 
gastric  juice,  which  flows  into  the  cavity  of  the  stomach. 

Chemical  analysis  shows  that  gastric  juice  contains, 
besides  tvater,  a  small  amount  of  salts,  a  little  free  hydro- 
eliloric  acid,  and  two  of  the  ferments,  called  j^ejysin  and 
rennin.  Renrmi  is  that  element  in  the  gastric  juice  which 
causes  milk  to  curdle.  The  use  of  rennet  (which  is  ob- 
tained from  the  stomach  of  a  calf)  in  the  making  of  cheese 
depends  upon  the  presence  of  this  ferment.  Pepsin  is 
the  ferment  Avhich  is  able  to  change  proteids  into  soluble 
form,  and  to  make  diffusible  such  as  are  not  already  so. 
The  ferments  of  the  gastric  juice  act  only  in  the  presence 
of  an  acid,  and  to  assist  their  action  seems  to  be  the  func- 
tion of  the  hydrochloric  acid. 

327.  The  Food  in  the  Stomach.  —  The  effect  of  the  gastric 
juice  upon  the  food  in  the  stomach  is  to  make  the  whole 


THE   DIGESTIVE   APPARATI^S   AND   NUTRITION       231 

mass  acid.  This  destroys  tlic  ptvalin,  and  no  more  starch 
is  converted  into  sugar.  As  the  saliva  acts  only  upon 
starch,  so  the  gastric  juice  acts  only  upon  the  proteids. 
By  the  muscular  movements  in  the  walls  of  the  stomach 
the  food  is  moved  from  side  to  side  and  thoroughly  mixed 
with  the  gastric  juice,  and  the  mass  becomes  semifluid. 
The  fats  and  carboh3'drates  remain  unchanged,  except  as 
affected  by  the  warmth  of  the  stomach  and  by  the  removal 
of  the  proteids  which  are  dissolved  out  of  the  mass. 

328.  Digestion  in  the  Small  Intestine.  —  The  food  by  re- 
maining in  the  stomach  from  one  hour  to  three  or  four, 
is  converted  into  what  is  called  chyme.  The  sphincter 
muscle  of  the  pyloric  orifice  relaxes  at  intervals,  and  the 
chyme  is  then  passed  on  into  the  small  intestine  by  the 
contractions  of  the  wall  of  the  stomach.  Here  it  soon 
encounters  two  other  juices,  the  hih  and  the  pancreatic 
juice,  by  which  it  is  still  further  changed. 

329.  The  Pancreas  is  a  long,  slender  gland,  enlarged  at 
its  right  end,  lying  back  of  the  stomach  and  along  its 
greater  curvature,  and  supported  by  the  mesentery  (Fig. 
9-4,  p.  163).  It  is  pinkish  yelloAv  in  color,  and  resembles 
the  salivary  glands  in  structure.  A  duct  runs  from  one  end 
to  the  other,  joins  the  common  bile  duct  from  the  liver, 
and  passes  with  it  obliquely  through  the  wall  of  the  small 
intestine  (Fig.  110). 

330.  The  Pancreatic  Juice.  —  The  pancreas  has  reflex 
nervous  connection  with  the  stomach,  and  as  soon  as  food 
enters  the  latter,  secretion  begins  in  the  pancreas,  and 
the  secreted  fluid  accumulates  in  the  small  intestine. 

The  pancreatic  juice  is  a  clear,  somewhat  viscid,  alkaline 
fluid,  containing  man}^  different  sul)stances,  the  most  im- 
portant being  the  ferments.     Of  these  there  are  four. 

One,    similar    to    pepsin,    but  able  to    act    only    in    an 


232  UNCONSCIOUS  NERVOUS   OPERATIONS 

alkaline  medium,  affects  the  proteids  more  rapidly  and 
more  powerfully  than  pepsin,  and  so  digests  those  which 
were  not  sufficiently  changed  by  the  gastric  juice. 

Another  ferment  in  the  pancreatic  juice  acts  like  the 
saliva  upon  starch,  converting  it  into  malt  sugar,  but  its 
action  is  far  more  powerful.  This  ferment  is  not  present 
in  the  pancreatic  juice  of  infants,  and  they  are  therefore 
unable  to  digest  starchy  foods  properly. 

The  pancreatic  juice  has  two  different  effects  upon  the 
fats,  they  having  hitherto  been  unchanged.  The  first 
effect  is  to  separate  them  into  exceedingly  small  particles, 
which  can  pass  through  the  walls  of  the  intestine,  that  is, 
the  juice  forms  an  emulsion  with  the  fat.  The  second 
effect  is  a  chemical  decomposition  of  fat  into  fattt/  acid 
and  glycerin  by  the  action  of  the  third  of  the  pancreatic 
ferments.  The  acids  set  free  unite  with  the  alkaline  sub- 
stances present  to  form  soaps. 

The  fourth  ferment  possesses  the  power  of  curdling 
milk,  as  does  rennin,  though  its  action  is  not  identical 
with  that  of  rennin.  It  is  able  to  act  upon  any  particles 
of  milk  which  have  by  any  possibility  escaped  the  influ- 
ence of  the  gastric  juice. 

331.  The  Secretory  Nerves  of  the  Pancreas  have  been  found 
to  be  fibers  of  the  vagus,  or  tenth  cranial  nerve,  which,  as 
already  mentioned,  are  stimulated  by  efferent  impulses  ex- 
cited in  the  brain  by  afferent  impulses  from  the  stomach. 

332.  Other  Functions  of  the  Pancreas.  —  In  addition  to 
its  office  in  connection. with  digestion,  experiments  have 
proved  that  this  gland  has  some  further  influence  upon 
the  general  condition  of  the  body  ;  but  what  that  influ- 
ence is,  is  as  yet  unknown. 

333.  The  Liver,  which  weighs  from  fifty  to  sixty-four 
ounces,  is  the  largest  gland  in  the  body.     It  lies  chiefly 


THE   DIGESTIVE   APPARATUS   AND   NUTRITION       233 

on  the  right  side,  immediately  under  the  arch  of  the  dia- 
phragm (Fig.  86,  p.  153).  The  peritoneum,  without 
entirely  covering  it,  adheres  closely  to  it  and  attaches  it 
to  the  diaphragm  and  other  parts.  By  a  deep  fissure  it 
is  separated  into  right  and  left  lobes  (Fig.  116).  The 
tissue  elements  of  the  liver  are  the  hepatic  cells,  and  all 
the  other  parts    contribute  to  their   support,  protection. 


Fig.  116.  — The  liver  seen  from  below. 


and  nutrition.  The  hepatic  cells  are  grouped  together  in 
little  masses  to  form  lobules,  which  are  permeated  by  the 
blood  capillaries  from  the  portal  vein  and  the  hepatic 
artery.  From  these  capillaries  the  blood  passes  to  a  small 
vein  which  unites  with  those  from  other  lobules  to  form  the 
hepatic  veins,  which  empty  into  the  inferior  vena  cava. 

334.  Blood  Supply  of  the  Liver.  —  The  liver  has  an  im- 
mense supply  of  blood.     That  which  is  brought  by  the 


234  UNCONSCIOUS   NERVOUS   OPERATIONS 

portal  vein  has  first  circulated  through  the  stomach,  the 
spleen,  and  the  intestmes  (Fig.  95,  p.  165),  and  has  been 
deprived  of  most  of  its  oxygen.  The  supply  of  arterial 
blood  through  the  hepatic  artery  is  relatively  small. 

335.  Functions  of  the  Liver.  —  One  of  the  functions  of 
the  liver  is  to  store  up  sugar,  or,  rather,  to  form  from  the 
sugar  brought  by  the  portal  vein  a  substance  called  gly- 
cogen^ which  is  readily  converted  again  into  sugar.  The 
protoplasm  of  the  hepatic  cells  possesses  the  power  of 
manufacturing  glycogen  from  carbohydrates  and  of  stor- 
ing it  up.  This  is  effected  by  means  of  a  ferment  found 
in  the  liver  ;  but  what  is  the  part  played  by  glycogen  in 
the  animal  economy  is  not  fully  determined.  Glycogen 
is  turned  into  sugar  again  and  supplied  by  the  liver  to 
the  blood  as  it  is  needed.  There  is  always  sugar  in  the 
blood,  but  more  than  a  small  amount  seems  undesirable. 
There  is  much  evidence  that  another  function  of  the  liver 
is  to  act  upon  the  nitrogenous  foods  in  some  manner 
resulting  in  the  production  of  the  waste  substance,  urea^ 
which  is  eliminated  by  means  of  the  kidneys.  A  third 
and  the  most  familiar  office  of  the  liver  is  the  formation 
of  hile.  This  is  stored  in  the  gall  bladder^  Ijii^g"  between 
the  two  lobes  on  the  under  side  of  the  gland  (Fig,  116). 
Still  another  function  of  the  liver  is  to  protect  the  system 
from  the  action  of  poisons  produced  by  the  processes  of 
digestion  or  by  defective  digestion.  These  are  arrested  or 
transformed  when  they  reach  the  liver. 

336.  The  Bile  is  secreted  from  the  portal  blood  as  a  yel- 
lowish, reddish  brown,  or  green  fluid,  according  to  the  pre- 
ponderance of  different  coloring  matters  which  are  formed 
by  the  liver  out  of  the  hemoglobin  of  the  red  blood  cor- 
puscles. It  is  alkaline  and  is  thought  to  have  antiseptic 
properties.     Bile  is  a  poison,  and  in  one  person  enough  is 


THE   DIGESTIVE   APPARATUS   AND   NUTRITION       235 

secreted  in  a  day  to  kill  three  men  ;  but  it  is  neutralized 
in  the  intestines,  in  the  liver,  in  the  tissues,  and  in  the 
blood.  Upon  the  food  with  which  it  mixes  in  the  small 
intestine  bile  seems  to  have  little  effect,  and  its  function 
there  is  supposed  to  be  mainly  to  assist  the  pancreatic 
juice  in  neutralizing  the  acid  in  the  chyme,  and  in  its 
further  action.  Secretion  of  the  bile  goes  on  continu- 
ally, but  it  passes  into  the  intestine  only  when  digestion 
is  proceeding.  At  other  times  it  is  carried  by  a  side 
branch  of  the  bile  duct  to  the  gall  bladder  and  there 
stored.    About  two  pints  of  bile  is  secreted  daily. 

337.  The  Intestinal  Juice  is  a  secretion  of  the  mucous 
membrane  of  the  small  intestine  itself,  and  contains  a 
ferment  which  changes  cane  and  malt  sugars  into  glucose, 
besides  having  possibly  further  action  upon  the  food. 

338.  Bacterial  Action.  —  There  have  been  found  to  exist 
in  the  alimentary  canal  certain  microorganisms  which 
modify  the  digestive  processes.  Bacteria  are  especially 
numerous  in  the  intestines.  The  antiseptic  gastric  juice 
destroys  bacteria,  or  neutralizes  their  action  in  the  stomach; 
but  some  escape  into  the  intestines,  where  they  multiply. 
Their  presence  is  shown  to  be,  under  normal  conditions, 
beneficial,  though  certain  forms  of  bacteria  produce  disease. 

339.  The  Peristaltic  Movements  of  the  Intestines.  —  By  suc- 
cessive contractions  and  relaxations  of  the  muscular  fibers 
in  the  two  muscular  layers  of  the  intestinal  wall,  a  wave- 
like motion  passes  along  the  whole  length  of  the  organ  and 
forces  the  contents,  from  the  constricted  to  the  relaxed 
portion,  slowly  on  into  the  large  intestine,  bringing  the 
different  substances  in  contact  with  the  absorbing  cells  in 
the  mucous  membrane. 

340.  Function  of  the  Large  Intestine.  —  Most  of  the  food 
which  can  be  used  in  the  body  is  absorbed  in  the  stomach 


236       UNCONSCIOUS  NERVOUS  OPERATIONS 

and  small  intestine,  so  that  what  is  left  to  pass  into  the 
large  intestine  is  indigestible  matter  and  the  remains  of 
the  juices.  The  tubular  glands  in  the  mucous  membrane 
here  absorb  what  is  left  of  nutrient  material  and  a  con- 
siderable amount  of  water,  which  is  carried  by  the  small 
veins  to  the  portal  vein.  The  residuum,  becoming  more 
solid  as  the  water  is  absorbed,  passes  into  the  rectum  and 
is  discharged  as  fceces.  The  chief  alteration  in  the  con- 
tents of  the  large  intestine  is  due  to  the  action  of  micro- 
organisms which  cause  chemical  changes,  giving  rise  to 
organic  acids. 

341.  Absorption. —  When  the  food  has  been  digested  it 
is  ready  to  be  absorbed.  It  cannot  be  used  for  the  sup- 
port of  the  body  until  it  reaches  the  blood,  and  there  are 
two  ways  by  which  it  may  reach  the  blood.  First,  it  may 
be  absorbed  directly  into  the  blood.  The  mucous  lining 
of  the  alimentary  canal  is  richly  supplied  with  absorbing 
cells.  Little  of  the  food,  however,  is  taken  up  in  the 
mouth  and  esophagus,  because  of  the  thickness  of  the 
epithelium  in  those  cavities,  and  because  the  food  passes 
quickly  through  them.  In  the  stomach,  and  especially  in 
the  small  intestine,  the  absorbents  are  very  numerous,  and 
a  large  amount  of  digested  food  passes  directly  into  the 
blood  stream  by  the  capillaries  through  the  columnar  cells 
of  their  epithelium  ;  while  the  walls  of  the  large  intestine 
also  absorb  food,  but  to  a  less  extent.  This  direct  pas- 
sage into  the  blood  is  now  regarded  as  the  more  important 
of  the  two  channels  of  absorption.  The  living  cells,  while 
allowing  water  and  soluble  salts  to  pass  through  them 
unchanged,  effect  certain  changes  in  the  organic  food 
materials  while  in  contact  with  them.  The  carbohydrates 
and  proteids  are  mainly  absorbed  into  the  blood  in  this 
immediate  way. 


THE   DIGESTIVE    APPARATUS   AND   NUTKITION       287 

342.  The  second  agent  of  absorption  is  the  li/mpli  cells 
in  the  tissues  of  the  walls  of  the  alimentary  canal.  It  is 
chiefly  by  the  lymphatics  that  the  fat  of  the  food  gets  into 
the  cir<3ulation.  Two  changes  are  effected  in  the  fats  by 
the  digestive  juices  in  the  small  intestine  to  prepare  them 
for  absorption  by  the  lymphatic  vessels,  which  are  in  the 
intestines  called  lacteah,  because  the  presence  of  fat  ren- 
ders the  fluid  they  contain  millcy.  First,  by  the  mixture 
of  the  bile  and  pancreatic  juice  with  the  food  an  emulsion 
is  formed  :  that  is,  the  fat  is  broken  up  into  minute 
particles,  which  float  in  the  liquid,  giving  it  a  milky 
appearance.  Secondly,  a  chemical  union  takes  place 
between  some  of  the  acid  fats  and  the  alkaline  secretions 
of  tlie  digestive  organs,  —  a  process  called  saponification^ 
which  is  the  making  of  soap.  The  digested  food  in  its 
milky  form  is  called  chyle,  and  this  is  collected  in  larger  and 
larger  tubes,  and  tinally  poured  by  the  great  thoracic  duct 
into  the  blood  of  the  jugular  vein.  Being  then  carried  to 
the  right  auricle  of  the  heart,  it  passes  to  the  right  ven- 
tricle and  thence  to  the  lungs,  in  whose  capillaries  it 
meets  with  the  oxygen  from  the  air,  and  having  returned 
to  the  left  side  of  the  heart  is  distributed  throughout  the 
system. 

343.  The  Lymphatic  Vessels  are  delicate  tubes  which 
drain  the  spaces  between  the  cells  of  the  tissues,  gradu- 
ally uniting  to  form  the  main  lymphatic  vessels,  of  which 
the  thoracic  duct  is  the  largest.  These  vessels  are  sup- 
plied with  numerous  valves,  like  those  of  the  veins,  to 
prevent  the  reflow  of  their  contents,  and  the  opening  of 
the  thoracic  duct  is  guarded  by  a  valve.  The  flow  of  the 
fluid  is  kept  up  by  the  pressure  in  the  capillaries,  which 
is  greater  than  is  the  pressure  in  the  veins  into  which  it 
is  emptied,   and  by  the  movements   of  the  body,  which 

macy's  phys.  — 15 


238  UNCONSCIOUS  NERVOUS   OPERATIONS 

constantly  cause  pressure  upon  the  tissues  and  so  force 
the  lymph  onward  in  the  vessels,  the  valves  preventing 
any  return. 

344.  Assimilation.  —  Though  the  food  has  been  masti- 
cated, digested,  and  absorbed,  it  has  not  yet  nourished 
the  body.  Still  another  process  is  needful  before  the 
new  material  becomes  part  of  the  continually  wasting 
tissues.  That  process  is  called  assimilation^  and,  though 
we  cannot  pretend  to  understand  it,  it  may  be  described 
as  the  action  of  the  living  cells  in  choosing,  appropriat- 
ing, and  building  into  their  own  substance  the  suitable 
elements  in  the  food-laden  fluid  which  comes  to  them 
from  the  alimentary  canal  and  from  the  lungs. 

Correlative  to  the  process  of  assimilation  is  the  destruc- 
tive process  by  Avhich  the  cells,  by  combustion  and  other 
chemical  changes,  break  up  and  send  out  as  waste  the 
substances  of  their  structure,  to  be  expelled  frqm  the 
body  as  excretions. 

345.  Hunger  and  Thirst.  —  We  associate  our  feelings  of 
thirst  with  a  dryness  of  the  mucous  membrane  of  the 
mouth  and  throat,  and  we  say  our  throats  are  "  parched  " 
when  we  are  very  thirsty.  But  under  ordinary  circum- 
stances the  feeling  of  thirst  arises  from  a  general  con- 
dition of  the  system,  in  which  the  throat  shares,  due  to 
a  lack  of  water  in  the  blood,  or  rather  in  the  lymph. 
Thirst  may  be  temporarily  relieved  by  moistening  the 
mucous  membrane  of  the  soft  palate.  Hence  follows  the 
inference  that  the  afferent  nervous  impulses  originate 
there,  and  are  caused  by  a  too  great  removal  of  water 
from  the  lymph  of  the  investing  membrane. 

Hunger  is  referred  in  our  consciousness  to  the  par- 
ticular locality  of  the  stomach,  and  that  organ  seems  to 
us  to  be  empty  when  we  are  hungry.     Indigestible  mate- 


THE   DIGESTIVE   ArPARATUS   AND   NUTRITION       239 

rial  introduced  into  the  stomach  may  for  a  time  relieve 
the  hunger,  as  will  a  very  small  quantity  of  food.  The 
special  sensation  of  hunger  appears  to  be  connected  with 
the  state  of  the  lining  membrane  of  the  stomach,  while  it 
must  be  ascriljed  in  a  more  general  sense  to  a  deficiency 
of  nutrient  matter  in  the  blood.  Hunger  may  be  alle- 
viated by  the  introduction  of  soluble  food  into  the  circula- 
tion, through  the  rectum,  or  through  the  absorbents  of  the 
skin,  but  the  relief  comes  more  slowly  thus  than  through 
the  stomach. 

The  nervous  path  of  hunger  sensations  has  not  been 
made  out.  The  vagus  is  regarded  as  the  sensory  nerve 
of  the  stomach,  but  it  is  said  that  both  vagus  nerves  may 
be  cut  and  the  sensation  of  hunger  be  unaffected.  The 
brain  centers  for  thirst  and  hunger  are  believed  to  be  in 
the  occipital  lobes  of  the  cortex,  but  they  have  not  been 
definitely  located. 

346.  Some  Practical  Points  connected  with  Nutrition.  —  In 
order  that  the  first  of  the  digestive  operations  may  be 
properly  performed,  it  is  necessary  to  have  a  good  set  of 
teeth  and  to  chew  thoroughly/  the  food  taken  into  the 
mouth.  The  intensely  hard  enamel  covering  the  exposed 
portion  of  the  teeth  is  a  full  protection  to  them  against 
all  dangers  under  proper  conditions  of  life,  and  under 
such  conditions  the  teeth  would  last  Avhile  life  lasts. 
That  this  is  true  is  shown  by  the  fact  that  nature  makes 
no  provision  for  restoring  or  improving  the  enamel  after 
it  is  once  formed.  Here  alone  the  special  cells,  whose 
office  it  is  to  form  the  peculiar  substance,  entirely  disap- 
pear when  their  work  is  once  completed.  In  all  the  other 
tissues  these  formative  cells  remain  to  continue  the  nutri- 
tion and  repair  of  the  tissues.  But  the  tooth  enamel, 
whose  growth,  except  in  the  wisdom  teeth,  is  complete 


240  UNCONSCIOUS   NERVOUS   OPERATIONS 

when  a  child  is  ten  or  eleven  years  old,  cannot  be  renewed 
or  improved  after  that  time.  It  is  therefore  of  the  utmost 
importance  that  young  children  should  be  fed  upon  food 
which  will  build  up  perfect  teeth.  Milk  should  be  largely 
relied  upon  for  the  first  three  years,  the  diet  to  be  varied 
during  the  third  and  after  years  in  accordance  with  sug- 
gestions given  in  the  chapter  on  Food.  Great  care  should 
be  taken  to  guard  children  against  attacks  of  what  are 
known  as  "  infantile  diseases,"  — measles,  whooping  cough, 
etc.,  which  sometimes  suddenly  arrest  or  disturb  the  gen- 
eral nutrition,  and  especially  that  of  the  teeth,  so  that  the 
enamel  becomes  rough  and  irregular,  and  the  teeth  are 
exposed  to  early  decay.  Another  point  should  receive 
special  attention.  It  is  observed  that  young  children 
who  live  a  life  of  excessive  nervous  activity,  with  over- 
stimulation of  the  brain,  are  particularly  liable  to  defect- 
ive development  of  the  enamel  of  the  teeth.  This  is  one 
among  many  reasons  which  make  imperative  a  quiet,  regu- 
lar life  for  children,  without  excitement  and  without 
undue  mental  activity. 

347.  But  even  perfect  teeth  may  be  injured  by  certain 
bacteria,  which  multiply  in  the  decaying  particles  of  food 
allowed  to  remain  in  the  mouth.  These  minute  organisms 
form  a  corrosive  acid  which  destroys  the  enamel  and  breaks 
down  the  tooth  substance.  If  the  teeth  are  perfect  and 
are  always  kept  perfectly  clean,  they  will  not  decay. 
They  should  be  thoroughly  brushed  —  the  upper  teeth 
downward,  the  lower  ones  upward  —  after  each  meal,  and 
a  thread  of  soft  untwisted  silk  floss  or  fine  strips  of  rubber 
should  be  drawn  back  and  forth  between  the  teeth  to  cleanse 
those  parts  which  a  brush  cannot  reach.  In  brushing  the 
teeth  a  powder  or  liquid  should  be  used  which  contains 
some  safe  germicide,  —  which  is  a  substance  destructive  to 


THE    DIGESTIVE    APPARATUS   AND   NUTRITION       241 

the  microorganisms  mentioned  above,  —  and    the   mouth 
should  be  well  rinsed  with  a  solution  of  the  same. 

348.  It  is  a  mistake  to  suppose  that  a  child  should  be 
supplied  with  soft,  pulpy  food.  Just  as  soon  as  the  first 
set  of  teeth  are  in  place,  he  should  have  a  fare  which  will 
require  vigorous  mastication.  He  should  not  be  allowed 
to  reject  bread  crusts  and  eat  only  the  soft  crumb,  nor 
should  his  bread  be  always  soaked  in  milk  or  gravy. 
Plenty  of  hard  '^  chewing  "  is  not  only  good  for  the  teeth; 
it  also  promotes  the  flow  of  the  saliva  necessary  to  diges- 
tion and  aids  in  the  development  of  the  jaws,  and  so 
helps  to  provide  room  for  the  second  set. 

The  teeth  should  be  under  the  care  of  a  competent  den- 
tist, who  by  yearly  or  semiyearly  examination  and  repair 
will  be  able  to  forestall  and  prevent  the  inroads  of  decay. 

349.  While  a  due  action  of  the  mechanism  of  mastica- 
tion is  to  be  sought,  that  overactivity  which  results  from 
the  hahit  of  chewing  tobacco  or  gum  is  to  be  avoided.  While 
a  sense  of  propriety  and  good  taste  should  alone  be  suffi- 
cient to  condemn  such  a  habit,  there  are  hygienic  rea- 
sons for  its  avoidance.  The  constant  stimulation  of  the 
salivary  glands  leads  finally  to  their  weakness  and  defect- 
ive action,  thus  laying  a  foundation  for  general  derange- 
ment of  digestion.  Many  dentists  also  regard  it  as  directly 
injurious  to  the  teeth. 

350.  Food  is  not  ready  for  the  action  of  the  gastric 
juice  until  it  has  been  finely  divided  by  the  teeth  and  all 
portions  well  moistened  with  saliva.  Slow  and  thorough 
mastication  is  therefore  necessary  to  perfect  digestion. 
Too  rapid  eating  not  only  shows  bad  manners,  but  also  is 
exceedingly  bad  for  the  health. 

351.  The  temperature  of  our  food  should  not  be  so  hot 
as  to  stimulate  unduly  the  glands  of  the  mucous   mem- 


242  UNCONSCIOUS   NERVOUS   OT^ERATIONS 

brane  of  mouth  and  stomach,  nor  so  cold  as  to  retard  the 
digestive  processes,  which  normally  require  a  temperature 
of  about  100°  F.  (38°  C.  ).  Ice  water  should  never  be 
drunk,  both  because  of  the  impurities  usually  found  in 
the  ice,  and  because  its  coldness  is  injurious  to  the  stom- 
ach. Very  large  quantities  of  any  liquid  taken  with  the 
food  may  dilute  the  gastric  juice  so  much  as  to  delay 
digestion  and  w^eaken  the  organs. 

352.  It  is  well  to  establish  and  adhere  to  regular  hours 
for  meals.  The  intervals  between  meals  should  be  long 
enough  to  permit  the  digestive  organs  to  rest  between 
their  periods  of  activity,  and  fresh  food  should  not  be 
taken  into  the  stomach  to  mix  with  that  partly  digested ; 
that  is,  "  eating  between  meals "  is  to  be  avoided.  A 
habit  of  continually  nibbling  at  dainties  is  extremely  per- 
nicious, and  may  give  rise  to  serious  and  perhaps  incur- 
able disease. 

353.  A  considerable  variety  in  diet  is  wholesome,  but  as 
a  rule  one  should  adhere  to  the  simpler  and  more  easily 
digested  kinds  of  food.  A  person  in  health  is  scarcely 
conscious  of  possessing  a  stomach,  but  injudicious  indul- 
gence may  so  disorder  the  natural  processes  that  they  will 
be  constantly  attended  with  discomfort  or  suffering. 

354.  It  is  impossible  to  prescribe  definite  rules  for  the 
quantity  of  food  to  be  taken  daily.  A  strictly  natural 
appetite  is  undoubtedly  a  safe  guide  ;  but  appetite  is  so 
often  and  so  early  perverted  that  it  is  seldom  reliable. 
Food  enough  must  be  taken  to  supply  the  daily  waste  of 
tissues.  Continuous  loss  of  weight  is  usually  a  seriously 
unfavorable  symptom.  During  the  natural  period  of 
growth  the  amount  of  food  must  l)e  sufficient  to  supply 
also  what  is  needed  for  the  full  development  of  the  body. 
One  living  a  life  of  physical  activity  requires,  as  a  rule, 


THE    DIGESTIVE    APPAKATUS   AND   NUTRITION       243 

more  food  than  one  engaged  in  .sedentary  occupations. 
Brain  workers,  however,  need  a  varied  and  generous  diet, 
and  along  with  it  great  care  should  be  taken  to  secure 
sufficient  outdoor  exercise.  jMore  food  is  called  for  in 
Avinter  than  in  summer,  and  more  of  the  carbohydrates  to 
supply  the  demand  for  additional  heat.  Those  who  work 
A'igorously  in  the  open  air,  and  especially  in  cold  climates, 
often  consume  prodigious  quantities  of  fats  without  injury 
to  digestion.  With  the  coming  of  old  age  the  vital  proc- 
esses in  general  are  carried  on  more  slowly ;  digestion  and 
especially  the  power  of  assimilation  are  enfeebled.  Less 
energy  is  called  for  as  the  activities  are  lessened,  and  less 
food  is  then  required,  with  longer  intervals  between 
meals.  Foods  rich  in  proteids  are  less  needful  and  should 
be  diminished  in  quantity,  while  those  which  yield  a  large 
amount  of  heat  should  be  substituted. 

355.  What  is  Alcohol?  —  All  organic  bodies  are  subject 
to  decay;  the  complex  compounds  of  which  they  are 
composed  are  broken  up  into  simpler  ones,  and  that 
which  was  living,  organized  matter  becomes  lifeless  and 
inorganic.  This  destruction  of  organic  tissue  is  due 
under  ordinary  circumstances  to  the  process  called  fer- 
mentation in  some  one  or  more  forms.  This  is  the  growth 
and  rapid  multiplication  of  minute  organisms,  of  which 
yeast  is  the  most  familiar  example.  When  the  decom- 
position of  organic  matter  takes  place  under  certain  con- 
ditions and  reaches  a  certain  stage,  it  is  Q,?i\lQd  putrefaction. 
This  is  always  attended  by  the  multiplication  of  the  low 
forms  of  life  known  as  bacteria,  and  by  the  production  of 
poisonous  and  ill-smelling  gases.  Another  form  of  fer- 
mentation is  that  which  occurs  in  the  juices  of  fruits, 
grains,  and  vegetables  which  contain  sugar;  and  is  called 
vinous  fermentation.     In  this  form  of  decomposition  the 


244  UNCONSCIOUS  NERVOUS   OPERATIONS 

fungus  known  as  the  yeast  plant  is  the  active  agent  in 
producing  the  changes  which  occur.  The  sugar  of  the 
fruit  or  plant  must  be  in  solution,  and  the  germs  of  the 
yeast  must  in  some  way  be  introduced. 

Alcohol  is  one  of  the  products  of  vinous  fermentation. 
It  is  composed,  like  sugar,  of  carbon,  hydrogen,  and  oxy- 
gen, but  in  proportions  different  from  their  proportions 
in  sugar.  The  drinks  which  contain  alcohol  differ  widely 
in  flavor  according  to  their  sources,  and  also  vary  in  the 
amount  of  alcohol  which  appears  in  them.  In  cider  and 
some  kinds  of  beer  the  proportion  may  be  as  low  as  2  per 
cent.  As  alcohol  is  a  very  volatile  fluid,  it  may  be  readily 
separated  from  the  other  substances  in  the  fermented 
liquor  by  the  process  called  distillation.  This  is  the  driv- 
ing off  of  the  alcohol  in  the  form  of  vapor  by  the  applica- 
tion of  heat,  and  its  recondensation,  by  cooling,  to  liquid 
again.  In  this  way  is  obtained  the  strong  alcohol  which 
is  mixed  with  various  coloring  and  flavoring  matters  to 
form  the  sjmHtuous  liquors  of  commerce.  Whether  a 
drink  contains  the  2  per  cent  of  alcohol  found  in  cider, 
or  the  50,  or  more,  per  cent  found  in  whisky,  or  the 
90  per  cent  of  "  cologne  spirits,"  the  alcoliol  is  in  all 
cases  identical  in  its  nature  and  properties. 

356.  Properties  of  Alcohol.  —  Pure  spirit,  or  "absolute 
alcohol,"  is  a  colorless,  volatile  liquid  with  a  strong  affin- 
ity for  water,  which  it  rapidly  absorbs  from  the  atmos- 
phere or  from  any  other  substance  containing  water  with 
which  it  comes  in  contact.  Alcohol  burns  readily  in  the 
open  air,  that  is,  it  is  quickly  oxidized  and  changed  in  its 
chemical  composition.  It  is  a  powerful  solvent,  dissolv- 
ing many  substances  not  soluble  in  water.  Though  itself 
the  product  of  fermentation,  it  is  a  preventive  of  putre- 
faction,—  that  is,  it  preserves  animal  tissue  from  decay, 


THE   DIGESTIVE   APPAKATUS   AND   NUTRITION       245 

—  and  introduced  in  sufficient  amount  into  a  liquid  in  a 
state  of  vinous  fermentation  it  destroys  the  power  of  the 
yeast  plant  to  multiply,  Avhile  in  smaller  quantities  it 
retards  the  growth  of  the  living  cells  in  direct  proportion 
to  its  amount.  When  by  the  decomposition  of  sugar  in 
vinous  fermentation  the  amount  of  alcohol  produced  has 
reached  14  per  cent,  no  further  growth  of  the  yeast  takes 
place.  That  proportion  of  alcohol  destroys  the  vitality 
of  the  living  cells.  It  is  thus  useful  as  an  antiseptic. 
Brought  in  contact  with  food  elements  outside  the  body, 
alcohol  is  found  to  harden  them  by  abstracting  the  water 
which  they  contain,  and  to  coagulate  the  albumin,  which 
is  thus  rendered  insoluble. 

357.  Is  Alcohol  a  Food  ?  —  Alcohol  contributes  nothing  to 
the  formation  of  tissue,  and  cannot,  therefore,  be  classed 
in  the  first  division  of  foods,  according  to  the  definition 
given  in  §  289.  As  it  is  now  proved  that  when  taken 
into  the  stomach  in  dilute  form  and  in  small-  quantities 
it  may  be  fully  oxidized,  producing  energy,  it  must  be 
reckoned  in  the  second  class  of  foods,  as  a  force  generator. 
For  its  stimulating  effect  it  must  also  be  included  among 
the  force  regulators.  It  acts  upon  the  digestive  glands, 
causing  them  to  pour  out  their  special  products  more 
rapidly,  and  so  seems  sometimes  to  assist  digestion. 

But,  although  alcoholic  drinks  in  very  small  amounts 
are  found  to  come,  strictly  speaking,  under  the  definition 
of  food,  in  that  they  ma}^  and  do  develop  or  regulate 
force,  they  possess  at  the  same  time  properties  so  j^eculiar 
and  so  dangerous  that  it  is  wise  to  exclude  them  wholly 
from  our  dietary,  and  use  them,  if  at  all,  only  under  the 
advice  of  a  skillful  physician  in  case  of  illness.  In  cer- 
tain abnormal  conditions  of  the  system,  Avhen  ordinary 
food  cannot  be  digested,  it  has  sometimes  been  found  that 


246  UNCONSCIOUS   NERVOUS   OPERATIONS 

an  alcoholic  drink,  not  requiring  digestion,  will  supply 
the  necessary  energy  to  sustain  life  until  the  diseased 
organs  have  time  to  regain  the  power  to  assimilate  better 
food.  But  to  the  healthy  body  there  is  no  need  of  such  a 
whip  and  spur,  and  the  stimulus  of  alcohol  upon  the  secre- 
tions of  the  digestive  tract,  frequently  applied,  is  likely  to 
result  in  overstimulation  of  the  organs,  and  consequent 
weakness,  with  a  long  train  of  evils  to  follow. 

As  a  food,  alcohol  is  of  little  value  compared  with  other 
substances.  It  is  more  expensive  than  almost  anything 
else  that  is  ever  used  as  food,  and  cannot  by  itself  sustain 
life  ;  for,  while  it  does  generate  a  certain  amount  of  energy, 
the  body  is  really  feeding  upon  the  stored-up  proteids, 
and  the  cost  of  the  few  spoonfuls  of  whisky  or  brandy,  or 
the  quart  of  beer  which  may  perhaps  be  drunk  without 
immediate  bad  effects,  would  buy  of  wholesome  bread  and 
meat  enough  to  produce  in  the  body  many  times  the 
amount  of  normal  force  which  the  alcohol  imparts. 

358.  Alcohol  as  a  Poison.  —  The  beneficent  use  of  alcoholic 
drink  seems  to  be  wholly  confined  to  its  application  as-  a 
medicine  to  diseased  conditions  of  the  system,  and  with 
that  sort  of  use  we  have  here  nothing  to  do.  It  has  been 
demonstrated  that  a  healthy  man  may  consume  drink,  in 
twenty-four  hours,  which  contains  from  two  to  two  and  a 
half  ounces  of  alcohol  without  apparent  injury,  when  all 
circumstances  are  as  favorable  as  possible  for  the  perfect 
action  of  all  the  bodily  organs.  But  it  by  no  means  fol- 
lows that  it  would  be  equally  safe  for  a  man  in  the  varying 
and  uncertain  conditions  of  ordinary  life  to  incur  the  risk 
of  disturbing  the  nice  balance  of  the  physical  adjustment 
upon  which  vigorous  health  depends  by  introducing  into 
his  organism  an  element  which  may^  and  more  likely  than 
not  ivill^  disorder  the  action  of  some  one  or  more  of  the 


THE   DIGESTIVE    APPARATUS   AND    NUTRITIOX       247 

delicate  organs.  Let  him  take  just  a  little  more  than  the 
exact  amount  which  can  be  at  once  oxidized  in  the  bk)od 
or  other  tissue,  and  it  is  carried  on  through  the  system  as 
alcohol,  to  work  its  characteristic  effects.  In  the  stomach 
the  alcohol  may  harden  the  albumin  of  the  food,  and  so 
prevent  its  complete  digestion.  If  strong  enough,  it  may 
attack  the  albumin  in  the  cells  of  the  lining  of  the  stomach 
itself.  This  is  the  reason  for  the  Avell-known  fact  that 
alcoholic  drinks  do  less  harm  if  taken  after  a  meal  than  if 
taken  on  an  empty  stomach.  A  large  quantity  of  strong 
drink  taken  at  once  seems  to  paralyze  the  nerves  control- 
ling the  absorbents  in  the  stomach,  and  often  results  in 
sudden  death.  Passing  into  the  circulation,  alcohol,  as  we 
have  already  seen  in  respect  to  yeast,  acts  directly  upon 
the  vitality  of  the  living  cells,  hindering  their  growth  and, 
when  strong  enough,  wholly  destroying  their  vital  power. 
Any  excess  beyond  the  amount  which  can  be  oxidized  at 
once  interferes  with  normal  cell  activity,  and  works  vari- 
ous physiological  evils,  as  pointed  out  in  diff'erent  chapters 
of  this  book.     All  these  are  the  actions  of  a  poison. 

359.  In  the  stomach  alcoholic  fluids  of  all  sorts  increase 
very  greatly  the  flow  of  gastric  juice,  and  it  would  appear 
that  this  stimulation  might  assist  digestion.  But  since 
the  alcohol  is  found  to  disappear  wholly  from  the  alimen- 
tary tract  within  half  an  hour,  this  direct  influence  upon 
the  secretion  of  gastric  and  other  digestive  juices  can  be 
but  slight.  Moreover,  excessive  or  abnormal  stimulation 
of  any  organ  results  ultimately  in  the  weakening  of  its 
functional  power.  In  the  healthy  animal  wholesome  food 
supplies  all  the  stimulus  needed  by  the  various  digestive 
organs. 

In  the  intestines  alcohol  is  rapidly  absorbed  into  the 
blood.     By  dilution  with  the  juices  of  the  mouth  and  the 


248  UNCONSCIOUS  NERVOUS   OPERATIONS 

stomach  its  power  for  direct  injury  lias  already  been  re- 
duced; but  if  the  work  of  the  stomach  has  been  imper- 
fectly done  because  of  its  presence,  more  labor  remains 
to  the  intestines,  and  that  may  disorder  the  whole  system. 
360.  The  portal  vein  carries  the  alcohol  absorbed  from 
the  stomach  and  the  intestine  directly  to  the  liver.  Here 
its  evil  effects  in  developing  disease  are  earliest  and  often- 
est  apparent.  Alcohol  in  the  liver,  as  in  other  places, 
greedily  uses  up  the  oxygen  needed  for  the  necessary  vital 
operations.  In  that  way  it  prevents  the  normal  action  of 
the  hepatic  cells,  for  not  enough  oxygen  remains  for  them 
to  do  their  work  perfectly.  Now  the  liver,  as  the  largest 
organ  in  the  body,  has  a  correspondingly  important  part  to 
play  in  the  vital  processes,  and  any  interference  with  its 
functions  is  extremely  serious.  It  is  well  known  to  physi- 
cians that  a  drunkard's  liver  presents  a  greatly  modified 
appearance,  which  is  seen  to  a  less  degree  in  the  liver  of  a 
moderate  drinker.  Alcohol  does  not  build  useful  tissue, 
but  instead  it  promotes  the  abnormal  deposit  of  fat  cells, 
causing  what  is  called  "  fatty  degeneration."  This  is  often 
seen  in  the  liver  of  alcohol  users  and  causes  enlargement 
of  the  organ;  the  connective  tissue,  also,  is  sometimes 
inflamed  and  hardened.  Because  of  the  imperfect  action 
of  the  liver,  poisons  which  should  have  been  neutralized 
are  allowed  to  circulate  through  the  system  and  undermine 
its  health. 

So  it  appears  that  throughout  the  digestive  tract  alco- 
hol is  liable  to  Avork  harm  to  the  organs  more  or  less 
serious  in  proportion  to  the  frequency  of  its  use  and  its 
amount. 

361 .  Other  Sources  of  Danger  from  Alcoholic  Drinks.  —  Many 
of  the  drinks  containing  alcohol  contain  also  a  mixture 
of  nutritious  substances,  such  as  unfermented  sugar  and 


THE   DIGESTIVE   APPARATUS   AND   NUTRITION       249 

other  foods  found  in  the  vegetables  used  in  the  manu- 
facture ;  though  no  one  drinks  those  beverages  for  the 
sake  of  the  trace  of  nourishing  matter  in  them.  But 
there  are  formed  along  with  the  alcohol  in  fermentation 
other  products,  some  of  which  are  known  to  be  directly 
poisonous,  while  others  are  at  least  probably  injurious. 
Fusel  oil  and  various  ethers  are  among  these  substances. 
Another  source  of  danger  is  found  in  the  frequent  adul- 
teration of  alcoholic  beverages.  The  great  expense  attend- 
ing their  manufacture  leads  to  the  use  of  inferior 
materials,  impure  sugars,  defective  fruits,  etc.,  and  to 
the  addition  of  poisonous  coloring  and  flavoring  matters. 
In  some  cases  even  so  virulent  a  poison  as  strychnine 
has  been  found.  These  adulterations  still  further  men- 
ace the  health  of  the  users  of  such  drinks. 

362.  The  Most  Dangerous  Quality  of  Alcohol.  —  Bad  as  it  is 
to  suffer  from  enfeebled  physical  conditions,  it  is  yet  worse 
to  become  weak  in  mind  and  unstable  in  moral  character. 
No  one  will  deny  that  such  weakness  and  instability  are 
results  of  the  excessive  use  of  alcoholic  liquors.  But  no 
man  ever  lived  who  deliberately  determined  to  make 
himself  a  drunkard,  when  first  beginning  to  taste  the 
exhilaration  of  the  moderate  use  of  such  beverages. 
Every  one  thinks  he  will  confine  himself  to  the  small 
quantity  which  he  believes  will  do  him  no  harm.  How 
is  it,  then,  that  in  all  the  great  cities  of  the  world  certain 
streets  are  by  night  full  of  the  sounds  of  crazy  drunken 
revelry;  that  prisons  are  crowded  with  criminals  made 
such  by  involuntary  acts  when  "in  liquor";  that  myriads 
of  human  beings  tumble  every  year  into  drunkards'  graves, 
dying  as  the  beast  dieth,  all  the  beauty  and  dignity  of 
life  wrecked  long  before,  all  hope,  all  possibility  of  rescue 
long  since  abandoned  ? 


250  UNCONSCIOUS  NERVOUS  OPERATIONS 

We  class  alcohol  among  the  foods  because  it  comes 
within  our  definition  of  food,  but  in  a  higher  degree  than 
any  other  substance  used  for  food,  it  possesses  a  peculiar 
power  which  is  not  characteristic  of  food.  It  is  the  power 
of  developing  a  progressive  craving,  an  uncontrollable 
appetite  for  itself,  which  is  never  satisfied,  and  which 
leads  the  wine  bibber  to  long  ever  for  more  and  stronger 
wine,  or  whisky,  or  gin,  or  brandy.  It  is  easy  to  say,  "  I 
will  never  drink  any  more  alcohol  in  a  day  than  the  two 
ounces  and  a  half  which  science  has  proved  can  be  wholly 
oxidized  in  the  body,  yielding  force  and  conserving  to 
the  extent  of  its  own  service  the  physical  powers."  The 
man  who  speaks  thus  may  indeed  be  able  so  to  regulate 
his  actions,  but  millions  of  his  fellow-men  have  not  been 
able  to  do  so.  Men  do  not  rightly  estimate  the  full  force 
of  the  insidious  power  of  alcohol  to  create  an  ever-grow- 
ing appetite  which  demands  ever  more  alcohol*  for  its 
satisfaction.  Bread  and  meat  and  milk  and  fruit,  which 
build  the  tissues  and  supply  the  forces  for  vigorous  and 
worthy  life,  do  not  create  an  abnormal  appetite  for  them- 
selves. Sometimes  a  man  or  a  woman  indulges  in  the 
excessive  use  of  tea  or  coffee,  and  may  possibly  experi- 
ence something  of  the  unhealthy  craving  for  those  bev- 
erages which  the  drunkard  has  for  his  liquor.  But 
harmful  as  the  effect  of  such  indulgence  is  upon  the 
physical  system,  it  does  not  so  undermine  the  mental  and 
moral  health  as  does  the  alcoholic  habit. 

363.  It  is  at  least  'perfectly  safe  to  avoid  wholly  the  use  of 
alcoholic  beverages.  One  who  does  so  is  certain  to  escape 
the  frightful  danger  of  acquiring  that  overmastering  appe- 
tite for  alcohol,  to  satisfy  which  he  might  become  willing  to 
commit  murder  or  arson,  or  any  other  crime,  and  for  whose 
indulgence  he  may  be  led  to  ruin  all  his  hopes  of  happi- 


THE   DIGESTIVE   APPARATUS   AND   NUTRITION       251 

ness  for  this  world  and  for  the  world  to  come,  and  crush 
out  all  joy  from  the  lives  of  those  dear  to  him.  What  is 
the  wise  course  for  a  being  endowed  with  reason  ? 

Demonstrations  and  Experiments 

111.  A  General  Dissection  of  the  Digestive  Organs  can  be  performed 
on  the  body  of  a  rat,  cat,  dog,  or  rabbit.  In  this  dissection  other 
viscera  besides  the  digestive  organs  should  be  examined.  Just  how 
much  of  the  dissection  is  to  be  done  by  pupils,  if  any  at  all,  must  be 
left  to  the  judgment  of  the  teacher.  Whether  the  actual  class  work 
takes  on  the  nature  of  a  dissection  or  merely  of  a  demonstration,  the 
attempt  should  be  made  to  examine,  as  far  as  possible,  every  organ 
described  in  the  text.  To  show  the  villi,  cut  out  a  piece  of  the  wall 
of  the  small  intestine,  and  after  gently  washing  it  examine  the  inner 
surface  with  a  hand  lens.  Teeth  of  various  animals  can  be  obtained 
to  show  the  arrangement  in  the  jaws  and  the  general  structure  and 
materials  of  a  tooth. 

112.  Minute  Structure  of  Digestive  Organs.  —  Some  prepared  micro- 
scopical sections  of  various  parts  of  the  digestive  tract  will  aid  the 
pupil  greatly  in  understanding  the  structure  and  properties  of  the 
alimentary  organs.  Very  instructive  are  sections  of  the  wall  of 
the  esophagus ;  of  the  stomach,  showing  the  three  muscular  coats ; 
of  the  small  intestine;  and  sections  of  a  salivary  gland  and  of  the 
liver.     Tissues  of  any  of  the  domestic  animals  can  be  used. 

Experiments  in  Digestion.  —  It  should  be  borne  in  mind  that  diges- 
tion carried  on  in  test  tubes  is  not  normal,  and  that  these  experi- 
ments in  digestion  are  merely  illustrative. 

113.  Salivary  Digestion.  — To  a  test  tube  about  half  full  of  starch 
solution  1  add  a  little  saliva  and  place  the  tube  where  the  temperature 
can  be  kept  at  about  37°  C.  (98°  F.).  In  a  few  minutes  the  starch 
solution  becomes  clear,  and  while  at  first  it  gave  the  characteristic 
reaction  with  iodine  it  now  no  longer  turns  blue,  but  if  Trommer's 
test  (Ex.  96)  be  applied,  turns  yellow,  showing  presence  of  sugar.     To 

1  Rub  a  gram  of  laundry  starch  into  a  paste  with  a  little  cold  water. 
Then  add  a  hundred  cubic  centimeters  of  boiling  water,  and  boil  for  a  few 
minutes.     Cool  before  using. 


252  UNCONSCIOUS   NERVOUS   OPERATIONS 

be  sure  that  the  sugar  is  a  product  of  digestion,  Trommer's  test 
should  be  applied  to  the  solution  before  saliva  is  added,  and  also  to 
dilute  saliva. 

Prepare  two  other  test  tubes  in  a  similar  way,  but  boil  the  contents 
of  one,  and  place  the  other  on  ice,  or  in  a  very  cool  place.  From  this 
conclusions  may  be  drawn  regarding  the  relation  of  temperature  to 
the  activity  of  the  ferment  of  saliva. 

The  saliva  of  some  persons  has  little  or  no  digestive  effect,  hence 
this  experiment  will  occasionally  fail. 

114.  Gastric  Digestion.  —  Fill  three  test  tubes  about  half  full  of 
artificial  gastric  juice.i  and  three  other  test  tubes  with  (1)  water,  (2) 
water  containing  a  little  powdered  pepsin,  and  (3)  a  j%  per  cent 
muriatic  acid  solution,  respectively.  Place  in  each  test  tube  a  few 
shreds  of  fibrin.  Fibrin  is  used  because  it  is  a  solid  proteid,  and 
the  progress  of  its  digestion  can  be  followed  with  the  eye,  without 
making  special  tests.  Boiled  white  of  Qgg  may  be  used,  but  it 
digests  more  slowly.  Boil  one  test  tube  containing  artificial  gastric 
juice,  place  a  second  on  ice,  and  set  away  the  other  test  tubes  in  a 
warm  (37°  C.)  place. 

In  a  short  time  the  fibrin  in  the  tube  of  gastric  juice  kept  in  the 
"warm  place  is  seen  to  be  much  swollen,  and  gradually  it  disappears 
in  solution.  Compare  the  test  tube  with  the  others.  What  effect 
has  temperature  on  gastric  digestion?  Is  the  presence  of  pepsin 
necessary?     Does  pepsin  alone  (in  water)  digest  the  fibrin? 

115.  Action  of  Gastric  Juice  on  Milk.  —  To  a  test  tube  about  half 
full  of  fresh  milk,  add  a  little  artificial  gastric  juice  that  has  been 
neutralized  by  the  addition  of  dilute  carbonate  of  soda.  Keep  at  a 
temperature  of  about  37°  C.  (98°  F.).  In  a  short  time  the  milk 
curdles.  In  previous  experiments  on  milk,  curdling  was  produced 
by  acids;  here,  since  the  gastric  juice  was  neutralized,  it  is  due  to 
some  other  cause.  To  the  test  tube  add  a  little  dilute  muriatic  acid  to 
acidulate  the  contents,  and  keep  it  in  the  warm  place  for  several  hours. 
The  casein  is  finally  digested  in  the  presence  of  acid,  forming  a  sti-aw- 
colored  fluid. 

116.  Action  of  Rennet  on  Milk.  —  To  some  fresh  milk  hi  a  test 
tube  add  a  little  commercial  extract  of  rennet,  and  keep  at  a  tempera- 

1  Add  a  little  powdered  pepsin  (to  be  obtained  at  a  druggist's)  to  a 
■^  per  cent  solution  of  muriatic  (hydrochloric)  acid. 


THE   DIGESTIVE    APPARATUS   AND   NUTRITION       253 

ture  of  about  37°  C.  The  milk  curdles  in  a  few  minutes.  In  the 
previous  experiment  tlie  milk  was  curdled  by  the  i-ennin  ferment  in 
the  artificial  gastric  juice. 

117.  Action  of  Pancreatic  Juice  on  Starch.  —  Repeat  Ex.  118,  using, 
instead  of  saliva,  artificial  pancreatic  juice. i 

118.  Action  of  Pancreatic  Juice  on  Proteids. —  Repeat  Ex.  114, 
using  artificial  pancreatic  juice  instead  of  gastric  juice,  and  carbonate 
of  soda  solution  instead  of  muriatic  acid. 

119.  The  Emulsifying  Effect  of  Pancreatic  Juice.  —  Rub  together, 
in  a  mortar,  some  olive  oil,  or  cod-liver  oil,  with  pieces  of  fresh  pan- 
creas. An  emulsion  results.  Shake  together  in  a  test  tube  some 
olive  oil  and  a  little  artificial  pancreatic  juice,  as  used  in  preceding 
experiments.  An  emulsion  occurs  as  before.  Boil  some  artificial 
pancreatic  juice  to  destroy  the  ferment.  It  still  forms  an  emulsion 
with  oil.  In  the  experiments  on  fats  (Exs.  97-100)  it  was  seen  that 
an  alkali,  or  a  soluble  proteid,  forms  an  emulsion  with  fats.  Natural 
pancreatic  juice  contains  both  alkali  and  proteids.  Hence,  even  when 
boiled,  pancreatic  juice  emulsifies  fats. 

120.  Bile.  —  Obtain  bile  at  a  slaughterhouse.  Observe  its  color. 
Test  with  litmus  paper.     It  is  neutral  or  alkaline  if  fresh. 

121.  Action  of  Bile  in  Fats.  —  Shake  some  olive  oil  in  a  test  tube, 
with  five  times  its  bulk  of  bile.  Make  a  similar  mixture  of  olive  oil 
and  water,  and  observe  in  which  case  the  emulsion  lasts  longer. 
Shake  up  bile  with  olive  oil,  to  which  a  little  oleic  acid  is  added. 
The  emulsion  lasts  longer  than  before. 

122.  Action  of  Bile  in  Filtration  and  Absorption.  —  Into  each  of  two 
small  funnels  of  exactly  the  same  size,  put  a  filter  paper.  Moisten 
one  with  water  and  the  other  with  bile.  Pour  into  both  equal 
amounts  of  almond  oil,  and  after  covering  to  prevent  evaporation,  set 
aside  twelve  to  fourteen  hours.  The  oil  passes  through  the  filter 
moistened  with  bile,  but  scarcely  at  all  through  the  other. 

1  Add  a  little  powdered  pancreatine  to  a  1  per  cent  solution  of  car- 
bonate of  soda.  Commercial  pancreatine  commonly  contains  both  the 
starch-digesting  ferment,  amylopsin,  and  the  proteid-digesting  ferment, 
trypsin. 


macy's  phys.  — 16 


CHAPTER   XVIII 

THE  DUCTLESS   GLANDS 

364.  The  ductless  glands  are  organs  whose  functions 
are  not  yet  well  understood.  Unlike  other  glands,  they 
do  not  form  a  definite  secretion  poured  forth  by  means  of 
ducts.  Some  of  what  we  call  "  true  glands  "  have  been 
shown  to  send  into  the  lymph  and  blood,  in  addition  to 
the  secretion  passing  through  their  ducts,  material  of  great 
importance  to  the  healthy  working  of  the  body.  This  is 
true  of  the  liver  and  of  the  pancreas,  though  thes§  addi- 
tional functions  are  only  partly  understood.  It  is  probable 
that  the  ductless  glands  have  similar  offices  in  the  economy 
of  the  system. 

365.  The  Spleen  (Figs.  94  and  95,  pp.  163  and  165).  — 
The  largest  of  these  peculiar  glands  is  the  spleen^  a  dark 
purplish  body  of  variable  size  and  spongy  texture,  lying  on 
the  left  side  of  the  abdominal  cavity,  just  below  the  stom- 
ach. In  the  meshes  of  the  tissue  of  the  spleen  is  a  soft  sub- 
stance called  spleen  pulp.  This  consists  largely  of  red 
blood  corpuscles  and  colorless  cells,  some  of  which  are  like 
the  white  blood  corpuscles. 

366.  The  Blood  Supply  of  the  Spleen.  —  The  splenic  artery, 
a  branch  from  the  aorta,  carries  an  abundant  supply  of 
blood  to  the  gland  (Fig.  94),  and  the  smallest  branches 
of  the  artery  open  directly  into  the  spleen  pulp.  This 
is  the  only  place  in  the  body  where   the   blood   comes 

254 


THE   DUCTLESS   GLANDS 


255 


into  actual  contact  witli  the  cells  and  fibers  of  a  tissue. 
The  veins  of  the  spleen  unite  to  form  the  splenic  veiji, 
which  carries  the  blood  into  the  portal  vein  and  so  to  the 
liver. 

367.  Functions  of  the  Spleen.  —  Little  is  yet  positively 
known  as  to  the  functions  of  the  spleen.  That  the  organ 
has  some  connection  with  digestion  is  shown  by  its  enlarge- 
ment as  soon  as  gastric  digestion  is  completed.  It  has 
also  some  close  relation  to  the  liver,  and  it  is  understood 
to  be  engaged,  like  the  lymphatic  glands,  in  the  manufac- 
ture of  white  corpuscles.  In  some  animals  it  forms  the  colored 
corpuscles  likewise,  but  we  do  not  know  whether  that  is 
true  of  the  human  spleen.  It  is  thought  by  some  that  the 
spleen  is  the  organ  where  the  red  corpuscles  which  are 
worn  out  undergo  disintegration,  their  coloring  matter 
being  carried  to  the  liver  and  there  used  to  form  the 
coloring  matter  of  the  bile. 

368.  The  Thyroid  Gland  is  a  body  whose  two  lobes  lie  on 
the  sides  of  the  trachea  (Fig.  117).  The  disease  called 
goiter  is  an  enlargement 
and  alteration  of  struc- 
ture of  the  thyroid,  and 
the  effects  sometimes  ex- 
tend to  the  impairmeiit 
of  muscular  and  nervous 
activity  and  to  a  semi- 
idiotic  condition  of  mind, 
resulting  in  death  if  the 
whole  gland  is  affected. 
The  diseased  condition 
may  be  relieved  or  cured 
by  grafting  a  portion  of  the  thyroid  gland  from  an 
animal  under  the  skin  of  the  afflicted  one,  or  by  adding 


Thyroid  Gland 
Carotid  A. 
Internal  Jugular 
Trachea 

Siispenaory  Ligart 
Innomi7iate  V. 


Thymus  Gland 
Lung 


Fig.  117.  —  Thyroid  and  thymus  glands 
of  an  infant. 


256 


UNCONSCIOUS  NERVOUS   OPERATIONS 


Cortex 
Medulla 
z--^-^Pyramids 


new  thyroid  tissue  to  the  food,  or  even  by  subcutaneous 
injection  of  the  juice  of  a  healthy  gland.  It  is  concluded 
that  the  gland  either  forms,  or  helps  to  form,  some  sub- 
stance needful  to  health,  or  has  some  place  in  the  destruc- 
tion of  deleterious  substances  in  the  system,  but  positive 
knowledge  in  respect  to  it  is  lacking. 

369.   The  Thymus  Gland  lies  in  the  thorax  beneath  the 
sternum  (Fig.  117).     It  is  a  small  organ,  weighing  only 

about  half  an  ounce  at  birth. 

-Suprarenal 

body  After  growing  with  the  body 
until  the  second  year  it  gradu- 
ally shrinks  away,  and  before 
the  age  of  sixteen  usually 
disappears.  Its  use  is  quite 
unknown.  The  thymus  of 
calves  and  lambs  forms  an 
article  of  food  called- sweet- 
bread. 

370.  The  Suprarenal  Capsules 
(Fig.  118)  are  small  organs 
Longitudinal  section  of  resting  on  the  upper  portion 
kidney.  of    the    kidneys.     They    are 

supplied  with  an  abundance  of  blood  vessels  and  nerve 
fibers  and  nerve  cells.  It  has  been  found  that  their 
removal  from  animals  is  invariably  and  quickly  fatal. 
All  that  can  yet  be  said  as  to  the  function  of  these  bodies 
is  that  they  appear  to  form  something  which  is  essential 
to  the  healthy  tone  of  the  muscles. 


Fig.  118. 


CHAPTER    XIX 

THE   ORGANS   OF  EXCRETION 

371.  We  have  already  learned  that  a  double  vital  proc- 
ess is  continually  carried  on  by  the  living  cells  in  the 
tissues  of  the  body.  One  side  of  this  vital  activity  is  the 
taking  up.  from  the  blood,  of  oxygen  and  the  nutrient 
material  which  the  blood  receives  from  the  food  in  the 
alimentary  canal,  and  it  results  in  growth  and  repair. 
The  other  side  of  cell  activity  is  the  oxidation,  or  decom- 
position by  burning  in  the  tissues,  of  worn-out  matter, 
and  its  return  to  the  blood  to  be  expelled  from  the  body. 
This  removal  of  waste  matter  from  the  blood  is  called  ex- 
cretion. The  waste  material  from  the  tissues  leaves  the  body 
under  three  principal  forms, —  as  carboti  dioxide,  wafer,  and 
urea.  The  Jungs,  as  we  have  seen,  not  only  supply  oxygen 
to  the  blood,  but  also  sfive  off  dailv  a  laro^e  amount  of  water 
and  carbon  dioxide.  Two  other  organs  also  have  the 
function  of  excretion.  They  are  the  ski7i  and  the  Mdneys. 
The  skin  gives  off  water  and  certain  salts;  the  kidneys 
remove  urea  and  other  nitrogenous  waste,  along  with  a 
large  amount  of  water. 

372.  The  Skin  as  an  Excretory  Organ.  —  AVe  have  studied 
the  skin  as  an  organ  of  sensation,  and  have  learned  some- 
thing of  its  structure  and  its  use  as  a  sense  organ  and  as 
a  protector  of  the  more  delicate  parts.  No\\  we  are  to 
studv  it  as  a  remover  of  waste. 


258  UNCONSCIOUS   NERVOUS   OPERATIONS 

373.  Structure  of  the  Skin.  —  It  will  be  remembered  that 
the  skin  is  composed  of  two  layers:  the  epidermis^  jom- 
posed  of  many  layers  of  cells;  and  the  dermis,  or  true 
skin,  in  which  are  found  the  papillae,  blood  vessels,  and 
nerves,  with  the  end  organs  for  touch  and  glands  of  differ- 
ent sorts  (Fig.  49,  p.  83). 

374.  Perspiration.  —  The  excretion  of  the  skin  is  called 
perspiration,  or  stveat,  and  consists  of  water,  a  little  dis- 
solved salt,  and  some  fat.  When  the  perspiration  is  evapo- 
rated from  the  skin  as  fast  as  it  is  secreted,  it  is  called 
insensible  ijerspiration;  but  if  the  quantity  is  larger,  so  that 
it  collects  upon  the  surface,  we  call  it  sensible  perspiration. 

When  the  amount  of  sweat  produced  is  scanty,  it  is  acid 
in  chemical  composition;  but  when  the  discharge  is  profuse, 
it  is  alkaline.  This  difference  is  understood  to  be  due  to 
the  mixture  of  the  products  of  the  sebaceous  glands  with 
those  of  the  siveat  glands.  The  former  are  extremely 
minute  glands  pouring  their  secretions  into  the  hair 
follicles.  Their  product  is  acid  and  fatty,  and  is  constant, 
or  nearly  so,  in  quantity,  while  that  of  the  sweat  glands  is 
alkaline  and  variable  in  amount. 

375.  The  Sweat  Glands  are  very  abundant  over  the  whole 
skin.  They  consist  of  coiled  tubes  lying  deep  in  the  der- 
mis, and  the  duct  of  each  reaches  the  surface  by  a  cork- 
screwlike channel. 

376.  The  Nerves  controlling  the  Sweat  Glands  are  of  two  or 
three  different  sets.  Those  affecting  the  blood  circulation, 
vasomotor,  diminish  the  secretion  of  sweat  by  narrowing 
the  size  of  the  blood  vessels,  and  increase  it  by  dilating 
them.  The  special  secretory  fibers,  when  stimulated, 
cause  production  of  perspiration.  Still  other  nerve  fibers 
supply  the  plain  muscle  fibers  of  the  glands  and  regulate 
the  expulsion  of  the  fluid.     All   these    nerve   fibers    are 


TITE    ORGANS   OF    EXCRETION  269 

found  in  tlie  same  nerve  trunks.  I'here  are  subsidi- 
ary nervous  centers  for  this  secretion  in  different  parts 
of  the  spinal  cord;  but  tlie  chief  center  controlling  the 
others  is  the  medulla  oblongata,  and  the  nerve  fibers  for 
the  sweat  glands  run  in  the  nerve  trunks  supplying  the 
different  parts  of  the  body.  For  example,  the  sciatic 
nerve,  supplying  the  muscles  of  the  leg,  carries  secretory 
fibers  to  the  sweat  glands  of  the  leg. 

377.  Functions  of  Perspiration.  —  By  means  of  the  sweat 
glands  waste  water  taken  from  the  blood  continually 
passes  into  the  air.  The  amount  varies  greatly,  but  may 
be  said  to  average  about  one  and  a  half  pints  daily.  A 
very  little  carbonic  acid  and  solid  matter  are  found  in 
the  sweat,  along  with  the  fat  from  the  sebaceous  glands, 
and  a  mere  trace  of  urea. 

Besides  the  removal  of  waste  matter,  another  important 
function  belongs  to  the  skin  in  connection  with  perspi- 
ration. It  is  well  known  that  as  water  passes  from  the 
liquid  to  the  gaseous  state  a  large  amount  of  heat  becomes 
latent,  and  this  heat  is  supplied  by  adjacent  bodies. 
Hence  it  is  clear  that  by  the  evaporation  of  the  perspi- 
ration the  surface  of  the  body  is  cooled,  and  the  sweat  thus 
becomes  a  regulator  of  the  temperature  of  the  body,  the 
amount  of  evaporation  depending  upon  the  state  of  the 
body  and  of  the  surrounding  air. 

The  amount  of  sweat  secreted  is  also  affected  by  nerv- 
ous impulses  from  the  emotional  centers  in  the  brain. 
Fear,  for  example,  sometimes  causes  profuse  sweating. 
Strong  muscular  activity,  developing  heat  and  stimulating 
the  circulation,  increases  perspiration.  A  low  temperature 
in  the  surrounding  air  constricts  the  blood  vessels  of  the 
skin,  and  so  diminishes  the  production  of  sweat  and  pre- 
vents loss  of  heat  from  the  surface. 


260 


UNCONSCIOUS  NERVOUS   OPERATIONS 


378.  The  Kidneys  (Fig.  118)  are  bean-shaped  organs, 
lying  on  each  side  of  the  lumbar  portion  of  the  backbone. 

They  are  dark  red  in  color, 
about  four  inches  long,  two 
and  a  half  broad,  and  about 
one  inch  in  thickness.  At 
the  center  of  the  concave, 
or  inner  edge,  of  each  kid- 
ney the  arteries  enter  and 
the  veins  leave  the  organ. 
The  arteries  are  branches  of 
the  aorta ;  the  veins  empty 
into  the  inferior  vena  cava. 
From  the  same  portion  of 
each  kidney  passes  another 
tube,  the  ureter^  which  con- 
veys the  urine  secreted  by 
the  kidneys  to  the  sac  called 
the  hladder^  in  the  lower 
part  of  the  abdomen,  for 
storage.  The  ureters  pass 
obliquely  through'  the  wall 
of  the  bladder,  so  that  return 
of  the  contents  of  the  latter 
is  prevented. 

379.  Structure  of  the  Kidneys.  —  By  dividing  a  kidney 
lengthwise  through  the  middle,  two  distinct  parts  may  be 
seen :  an  outer,  granular  portion,  called  the  cortex^  lyi^^g 
next  to  the  inclosing  capsule,  and  an  inner  medullary  por- 
tion (Figs.  118  and  120).  The  latter  consists  of  a  number 
of  conical  parts,  called  pyramids^  with  their  bases  toward 
the  cortex.  In  the  cortical  portion  the  tiny  uriniferous 
tubules  commence  around  tufts  of  blood  capillaries  (^ylo- 


Fig  119— The  kidneys  and  bladder 
viewed  from  behind. 

A  aorta,  from  which  the  renal  arter- 
ies extend  to  the  kidneys. 

V  inferior  vena  cava,  from  which  the 
renal  veins  extend  to  the  kidneys. 

u  ureters. 


THE   ORGANS   OF   EXCRETION 


261 


meruli)  and  are  gathered  by  a  complicated  arrangement 
into  larger  divisions,  and  finally  empty  into  the  enlarged 
upper  portion  of  the  ureter.  From  the  little  bunches  of 
capillaries  spreads  throughout 
the  cortex  a  fine  network  of 
capillary  tubes,  which  gather 
into  veins  and  pour  the  blood 
into  the  renal  vein. 

380.  Nervous  Supply  of  the 
Kidneys. — The  kidneys  receive 
nerves  from  the  renal  plexus 
upon  each  side.  This  is  com- 
posed of  both  white  and  gray 
nerve  fibers  and  of  nerve  cells. 
They  come  from  many  sources, 
but  mainly  from  the  sympa- 
thetic   system     by    way    of  the     Fig.  120. -Diagram  of  a  longi- 

,  ,  ™,  ,     ,  tudinal  section  of  a  kidney, 

solar  plexus.        Ihe  renal  plexus  ^^  renal  artery. 

has    thus    indirect     connection  ^  capillaries. 

with  the  vagus  and  with  other  f  uri^feTous'tubuie. 

nerves  distributed  to  the  inter-  ^  ^^nai  vein. 

nal  organs.      These  nerves  seem  to  have  only  vasomotor 

functions.     As   yet,   we   are  unable  to  trace  the  special 

secretory  nerves   of  the  kidneys. 

381.  Functions  of  the  Kidneys.  —  The  food  which  we  eat, 
after  rendering  to  the  tissues  of  the  body  its  proper  serv- 
ice, is  converted  into  the  waste  products  ivater,  carbon 
dioxide,  small  quantities  of  salts,  and  urea  (or  some  sub- 
stance closely  allied).  The  first  two  excretions  result 
from  decomposition  of  the  carbohydrates  and  fats,  while 
from  the  proteids  come  certain  salts  and  nitrogen.  These 
last  are  excreted  almost  wholly  by  the  kidneys,  along 
with  a  large  quantity  of  Avater  and  a  very  little   carbon 


262  UNCONSCIOUS  NERVOUS   OPERATIONS 

dioxide.  To  the  kidneys,  then,  belongs  the  important 
function  of  removing  from  the  body  the  waste  product 
of  nitrogenous  food  in  all  the  living  tissues. 

382.  Urea.  —  The  final  result  of  the  changes  which 
nitrogenous  foods  undergo  is  urea^  and  its  chief  ultimate 
source  is  the  most  abundant  tissue  —  muscular  tissue. 
There  is,  however,  no  urea  in  the  muscles.  Other  steps 
in  its  production  lie  between  the  muscles  and  the  kidneys. 
The  spleen,  lymphatic  glands,  and  other  glands  have  to  do 
with  its  formation,  but  the  final  and  most  distinctive  changes 
appear  to  occur  in  the  liver.  If  the  urea  is  not  removed 
from  the  system,  it  destroys  life.  The  quantity  daily 
secreted  by  the  human  organism  is  about  five  hundred 
grains,  which  is  normally  2  per  cent  of  the  total  excre- 
tion from  the  kidneys. 

383.  Relation  between  the  Kidneys  and  the  Skin.  —  The 
relation  between  the  skin  and  the  kidneys  is  such  -that  if 
one  channel  of  excretion  becomes  clogged,  extra  labor 
appears  to  be  thrown  upon  the  other.  If  perspiration  is 
checked,  there  is,  along  with  diminished  activity  of  the 
sweat  glands,  constriction  of  the  blood  vessels  of  the  sur- 
face, followed  by  dilation  of  those  of  the  viscera,  which 
permits  an  increased  flow  of  blood  in  the  internal  organs, 
including  the  kidneys.  The  secretion  of  the  kidneys,  there- 
fore, becomes  more  abundant.  When  by  warmth  or  exer- 
cise the  sweat  glands  are  stimulated,  the  reverse  is  the  case  : 
the  vessels  of  the  skin  are  dilated,  while  those  of  the  abdo- 
men are  constricted,  and  the  renal  secretion  becomes  scanty. 

384.  The  Kidneys  and  the  Alimentary  Canal.  —  Still  more 
important  seems  to  be  the  connection  between  the  amount 
of  the  kidney  secretion  and  the  water  absorbed  by  the 
walls  of  the  alimentary  canal.  When  a  large  quantity  of 
water  is  drunk,  it  passes  directly  into  the  circulation,  and, 


THE  ORGANS  OF  EXCRETION  263 

though  the  general  blood  pressure  is  not  raised,  it  does 
appear  to  affect  directly  the  action  of  the  kidneys  and  to 
increase  the  excretion. 

385.  The  Kidneys  and  the  Nervous  System.  —  The  state  of 
the  central  nervous  system  greatly  affects  the  activity  of 
the  kidneys.  This  may  be  by  the  passage  of  emotional 
impulses,  originating  in  the  brain,  along  vasodilator  fibers 
to  the  kidneys.  The  blood  vessels  being  thus  dilated,  the 
activity  of  the  glands  would  be  stimulated.  Very  large 
quantities  of  almost  pure  water  are  sometimes  thus  elimi- 
nated under  emotional  excitement. 

386.  Excretion  by  the  Alimentary  Canal.  —  Portions  of  the 
food  taken  into  the  stomach  are  unfit  to  enter  into  the 
structure  of  the  tissues,  and  are  expelled  unchanged 
through  the  intestines.  A  small  amount  of  true  excretion 
also  takes  place  there,  by  which  used-up  matter  is  removed. 

387.  Autointoxication,  or  Self-poisoning.  —  Even  under 
normal  conditions  man's  organism  is  ''  a  receptacle  and  a 
laboratory  of  poisons."  They  are  taken  in  with  the  food 
in  the  form  of  those  minute  bodies  which  cause  putrefac- 
tion. The  process  of  katabolism  (§  283)  is  a  manufacture 
of  poisons,  and  many  of  the  secretions,  such  as  the  saliva 
and  the  bile,  are  poisonous.  A  large  number  of  poisonous 
substances  are  formed  in  the  intestines,  and  several  forms 
of  deadly  poison  have  been  discovered  in  the  urine.  All 
of  the  poisons  made  by  the  tissues,  and  some  of  those 
manufactured  in  the  digestive  tube,  are  poured  into  the 
blood,  so  that  even  normal  blood  contains  poisons,  though 
an  excessive  amount  of  the  same  poisons  threatens  health 
and  life.  Many  diseases  are  now  understood  to  result  from 
the  self -poisoning  due  to  disordered  nutrition,  along  with 
the  opportunities  for  infection  from  specific  germs  which 
are  always  present;  and  reabsorption  of  excrementitious 


264  UNCONSCIOUS   NERVOUS   OPERATIONS 

matter  once  separated  from  the   blood  for  rejection  is  a 
danger  to  be  guarded  against. 

388.  Attention  has  already  been  called  to  some  of  the 
ways  by  which  man  is  protected  from  the  injurious  prod- 
ucts of  his  own  organism  (§§  335,  336,  338).  The  gastric 
juice  contains  more  than  enough  hydrochloric  acid  to 
prevent  all  fermentation  in  the  stomach ;  but  in  the 
intestines  its  action  is  neutralized  by  the  alkalis  of  the 
intestinal  juices.  In  the  intestines  a  variety  of  poisons 
are  found,  and  when  digestion  is  disordered  the  num- 
ber and  quantity  may  be  dangerously  increased.  Some 
of  these  are  excreted,  while  others  are  absorbed  into  the 
blood.  The  liver  is  the  great  defense  against  the  poisons 
in  the  blood,  many  of  which  are  caught  by  that  gland, 
and  either  transformed  or  passed  on  to  be  removed  from 
the  body  by  means  of  the  kidneys.  By  the  lungs 
enough  carbon  dioxide  is  removed  from  the  body  every 
day  to  poison  a  man  to  death  many  times  over  ;  but  other 
injurious  matters  are  found  in  expired  air,  especially  in 
the  case  of  persons  suffering  from  defective  nutrition. 
The  skin  also  plays  its  part  in  the  elimination  of  poisons, 
and  the  peculiar  odor  of  the  perspiration  in  certain  abnor- 
mal conditions  is  a  guide  to  the  physician  as  to  the 
internal  state  of  the  system. 

All  these  facts  show  the  immense  importance  of  keep- 
ing constantly  open  and  in  healthy  condition  the  various 
channels  of  excretion. 

389.  Influence  of  Alcohol  upon  Excretion.  —  If  the  waste 
substances  constantly  formed  in  the  body  are  not  promptly 
removed,  they  tend  to  poison  the  system.  When  the  or- 
ganism is  at  a  high  level  of  health,  the  breaking  down  of 
tissue  by  oxidation,  which  produces  waste,  goes  on  rapidly 
and  vigorously.     When  this  is  retarded,  as  we  have  seen 


THE  ORGANS  OF  EXCRETION  265 

it  to  be  when  alcohol  is  introduced  into  the  circulation 
and  uses  up  the  oxygen  which  should  be  applied  to  the 
oxidation  of  food,  then  the  weight  may  increase,  but  it 
is  by  the  retention  of  poisonous  matter  which  ought  to 
be  removed.  No  other  one  cause  creates  so  much  disease  of 
the  kidneys  as  does  the  use  of  alcohol.  Imperfect  oxida- 
tion of  food  develops  poisons  which  the  kidneys  are 
overtaxed  to  remove.  This  may  be  caused  by  eating  too 
much,  or  by  eating  unwholesome  food,  or  too  much  of 
certain  kinds  of  food,  as  sugar  especially;  or  it  may  be 
caused  by  alcohol.  ''  Fatty  degeneration  of  the  kidneys  " 
is  a  frequent  result  of  the  use  of  alcoholic  drinks.  The 
cells  of  the  tissues  become  so  altered,  also,  that  they  fail 
to  act  normally  by  removing  only  the  poisonous  sub- 
stances, and  they  allow  the  valuable  elements  in  the  blood 
to  be  drained  off  with  the  waste.  This  is  seen  in  the 
serious  disease  called  "  Bright's  disease "  in  which  the 
albumin  which  is  necessary  to  health  is  excreted  by 
the   kidneys. 

Demonstrations 

123.  Dissection  of  the  Kidney.  —  Procure  a  kidney  of  a  sheep  or  of 
a  pig.  As  much  as  possible  of  the  ureter  should  remain  attached. 
The  kidney  is  seen  to  be  inclosed  in  a  capsule.  Remove  the  latter, 
and  notice  the  shape  of  the  kidney  and  the  enlarged  attachment  of 
the  ureter.  Split  the  kidney  lengthwise  parallel  to  the  broad  surface, 
and  observe  on  the  outside  of  the  section  a  layer,  the  cortical  layer, 
differing  in  color  from  the  more  internal,  medullar ij.,  portions,  i^otice 
the  projections,  pyramids,  of  the  medullary  portion  into  the  sinus. 
The  latter  is  a  cavity  in  the  concave  side  of  the  organ,  continuous 
with  the  cavity  of  the  ureter. 

124.  Minute  Structure  of  the  Kidney. —  For  this  some  prepared  sec- 
tions will  be  needed :  (1)  section  showing  general  structure  of  cortex 
and  medulla,  with  uriniferous  tubules  plainly  demonstrated  ;  (2)  sec- 
tion showing  blood  vessels  injected ;  (3)  a  cross  section  of  the  ureter. 


CHAPTER  XX 

THE  HEAT   OF   THE  BODY 

390.  Inanimate  bodies  tend  constantly  to  assume  the 
temperature  of  the  air,  water,  or  other  objects  near  them. 
An  object  which  has  been  heated  gives  out  heat  to  sur- 
rounding objects  until  all  are  of  the  same  temperature. 
There  is,  as  we  say,  a  tendency  to  equilibrium  in  respect 
to  temperature. 

391.  Animal  Heat.  —  Warm-blooded  animals  (birds  and 
mammals)  maintain  within  their  bodies,  summer  and  win- 
ter and  indoors  and  out,  with  slight  variations,  the  same 
degree  of  heat,  and  are  independent  of  their  surroundings 
in  that  respect. 

392.  Temperature  of  the  Body.  —  In  order  that  the  vital 
processes  necessary  to  human  health  and  comfort  may  go 
on  under  the  most  favorable  circumstances,  it  is  necessary 
that  the  body  should  maintain  a  temperature  of  from  98° 
to  99°  F.  (from  36.6°  to  ^7.2°  C).  If  it  rises  much  above 
or  sinks  much  below  this,  it  is  an  important  indication  of 
abnormal  condition  in  some  part  of  the  system.  We  may 
be  exposed  to  extreme  heat  and  to  severe  cold  without  any 
marked  change  in  the  bodily  heat.  The  skin,  it  is  true, 
being  in  contact  with  external  objects,  is  usually  cooler 
than  other  parts.  Some  of  the  internal  organs  have  in 
health  a  temperature  several  degrees  higher  than  the  gen- 
eral average,  and  any  special  activity  of  an  organ  develops 

266 


THE  HEAT  OF  THE  BODY  267 

a  local  excess  of  heat.  A  group  of  muscles,  for  instance, 
by  their  contraction,  produce  heat.  A  gland,  by  the  act 
of  secretion,  does  the  same.  But  the  tide  of  blood,  flow- 
ing swiftly  through  the  system  and  bathing  every  part, 
tends  to  equalize  the  heat  throughout. 

393.  The  Sources  of  Animal  Heat  are  of  two  sorts,  —  direct 
and  indirect.  The  great  source  of  heat  is  the  combustion 
of  food,  that  is,  the  oxidation  which  takes  place  in  the 
living  cells  in  all  parts  of  the  body.  This  is  equal  to  the 
amount  of  heat  which  would  be  given  off  by  the  burning 
in  the  open  air  of  the  same  quantity  of  food  Avhich  is  con- 
sumed in  the  body.  The  muscles  and  the  glands  are  the 
parts  in  which  the  greatest  amount  of  oxidation  takes 
place.  Some  little  heat  is  also  received  by  the  body  in 
hot  foods  and  drinks. 

Heat  is  produced  indirectly  by  the  transformation  of 
other  forms  of  energy.  Friction  of  one  part  upon  another 
—  as  of  the  blood  along  the  walls  of  the  blood  vessels  — 
becomes  heat.  All  mechanical  work,  all  nervous  activity, 
and  the  slight  manifestations  of  electricity  within  the 
body  liberate  heat. 

394.  Regulation  of  Temperature  is  accomplished  in  two 
ways;  viz.  by  variation  in  the  loss  of  heat  and  by  varia- 
tion in  its  production. 

Variatio7i  in  loss  of  heat.  Everything  which  leaves  the 
body  carries  away  a  portion  of  its  heat.  The  expired  air, 
the  perspiration,  the  excretions,  are  sources  of  loss  ;  and 
radiation  and  conduction  of  heat  from  the  surface  are  con- 
tinually going  on,  as  well  as  evaporation  from  the  skin  and 
the  lungs.  The  skin  is  the  chief  regulator  of  loss.  By 
clothing  the  body  a  portion  of  the  loss  by  radiation  is  pre- 
vented, and  we  have  already  seen  (§  376)  how  the  secre- 
tion of  sweat,  and  hence  the  cooling  of  the  surface  by 


268  UNCONSCIOUS  NERVOUS   OPERATIONS 

evaporation,  is  affected  by  the  vasomotor  and  nervous 
mechanisms  of  the  skin. 

Variation  in  production  of  heat.  The  processes  of  diges- 
tion are  attended  by  the  setting  free  of  heat.  The 
temperature  rises  after  a  meal,  while  a  marked  condition 
in  starvation  is  the  fall  of  the  bodily  temperature.  JNIus- 
cular  contraction  always  going  on  develops  heat,  and  the 
more  active  the  muscles  are,  the  greater  is  the  amount 
of  heat  produced. 

There  is  also  evidence,  from  numerous  experiments, 
of  direct  nervous  control  over  the  production  of  heat. 
Afferent  impulses  from  the  skin  or  other  organs  reach  the 
central  nervous  system  and  some  restricted  "  heat  center  " 
not  yet  anatomically  made  out  in  the  central  part  of  the 
brain.  The  exact  path  of  these  impulses  is  not  yet  ascer- 
tained. The  stimulation  of  the  heat  center,  wherever  it 
may  be  placed,  gives  rise  to  efferent  impulses  bj^  which 
activity  in  the  tissues  is  increased  and  heat  is  produced. 

395.  ClotMng.  —  Though  the  body  is  able  to  endure  a 
large  amount  of  exposure  to  heat  and  cold  without  injury, 
yet  the  mechanism  for  heat  production  may  be  overtaxed, 
as  well  as  the  digestive,  the  muscular,  or  the  nervous 
system.  Any  such  overtaxing  interferes  with  the  other 
functions  of  the  bod}^  Excessive  exposure  to  cold,  or 
insufficient  clothing,  forces  the  body  to  use  an  undue 
amount  of  energy  in  manufacturing  heat,  and  other  parts 
of  the  vital  economy  suff'er  ;  growth  in  the  young  is  inter- 
fered with,  and  mental  and  muscular  effort  become  diffi- 
cult. The  clothing  worn  should  therefore  be  such  as  will 
assist  in  preserving  the  natural  temperature  of  the  body, 
and  the  amount  and  the  material  will  vary  with  climate 
and  season,  as  well  as  with  the  age,  habits,  and  health 
of  the  wearer. 


THE   HEAT  OF  THE   BODY  269 

While  clothing  is  designed  to  prevent  too  rapid  radia- 
tion of  heat  from  the  surface,  it  should  still  permit  the 
evaporation  of  perspiration,  for  an  accumulation  of  mois- 
ture upon  the  skin  may  expose  one  to  dangerous  chills. 

396.  Fabrics  of  ivool  have  been  found  to  possess  more 
fully  than  any  other  materials  the  qualities  desired  for 
clothing.  They  are  so  light  and  porous  as  to  admit  of 
sufficiently  free  evaporation  and  the  circulation  of  air  ; 
and  as  wool  is  a  bad  conductor  of  heat,  it  retains  the  heat 
of  the  body,  while  it  holds  in  its  meshes  a  considerable 
quantity  of  air,  which  is  also  a  nonconductor  of  heat.  In 
variable  climates,  such  as  that  of  our  Northern  states,  it  is 
wise,  at  least  for  those  in  delicate  health  or  especially 
sensitive  to  changes  of  temperature,  to  wear  wool  next 
the  skin  at  all  seasons.  The  gentle  friction  of  woolen 
garments  against  the  skin  tends  to  prevent  clogging  of 
the  pores,  to  promote  even  circulation,  and  in  general  to 
keep  the  surface  in  a  healthy  condition. 

397.  Silk  is  less  valuable  than  wool  in  preserving  heat 
and  permitting  evaporation,  though  better  than  cotton  or 
linen.  It  may  be  worn  next  the  body  when  wool  causes 
irritation  of  the  skin. 

398.  Linen  is  less  usefuUthan  other  materials  for  the 
innermost  garments,  as  it  quickly  becomes  saturated  with 
moisture.  Cotton^  being  more  porous,  answers  the  purpose 
better.  In  respect  to  all  these  materials  the  weaving  of 
the  fabric  has  much  to  do  with  its  value  for  clothing. 
Closely  woven  cloth  of  hard-twisted  threads  should  not  be 
chosen  for  underwear,  but  rather  that  of  soft,  loosely 
twisted  fibers,  loosely  woven. 

399.  Fur  is  indispensable  in  the  coldest  climates,  as  it 
retains  better  than  anything  else  the  bodily  heat.  But  it 
prevents  the  evaporation  of  perspiration,  and  should  not 

macy's  phys.  —  17 


270  UNCONSCIOUS  NERVOUS   OPERATIONS 

be  worn  in  moderate  weather  ;  nor  should  fur  garments 
be  retained  indoors  —  as  when  sitting  in  an  assembly 
room.  The  practice  of  muffling  the  throat  in  wraps  of 
fur  should  be  avoided,  as  liable  to  render  the  larynx 
unnecessarily  sensitive  to  cold,  and  to  cause  the  evil  it 
is  intended  to  prevent. 

400.  Waterproof  wraps,  which  prevent  the  escape  of  per- 
spiration, should  be  worn  only  as  a  protection  from  rain  or 
snow. 

401.  Light-colored  clothing  reflects  the  rays  of  heat  and 
absorbs  but  little  warmth,  while  dark  colors  absorb  heat 
and  reflect  little.  Hence  the  common  custom  of  wearing 
light-colored  garments  in  summer  and  dark  ones  in  winter 
is  founded  in  reason. 

402.  Frequent  changes  of  clothing,  especially  of  that 
which  touches  the  skin,  are  needful.  The  pores  of  a 
fabric  soon  become  filled  with  the  poisonous  wagte  mat- 
ters secreted  by  the  skin.  The  clothing  worn  by  day 
should  never  be  worn  during  the 'night  also.  If  it  is  to 
be  resumed  in  the  morning,  it  should  be  exposed  to  free 
circulation  of  air  during  the  night.  Night  clothes  and 
all  bedding  should  be  carefully  sunned  and  aired  each 
day. 

403.  It  is  important  that  all  clothing  and  bedding 
should  be  thoroughly  dry.  Damp  clothes  do  not  retain 
the  natural  heat  of  the  body,  but  rapidly  conduct  it  away, 
leaving  the  surface  chilled  and  the  system  exposed  to 
attacks  of  disease.  Especially  should  shoes  and  stockings 
which  have  become  wet  be  removed  as  soon  as  possible. 
Many  a  serious  or  fatal  illness  has  resulted  from  neglect 
of  this  precaution.  Damp  bedding  is  especially  dangerous 
to  health,  as  the  relaxed  condition  of  the  body  during 
sleep  renders  it  an  easy  prey  to  every  cause  of  disease. 


THE  HEAT  OF  THE  BODY  271 

404.  Care  should  be  exercised  in  changing  from  the 
warm  clothing  of  winter  to  the  thinner  garments  needed 
in  the  spring.  It  is  most  prudent  to  make  changes  first 
in  the  outer  clothing,  retaining  the  warm  inner  garments 
until  the  mild  weather  is  well  established.  Often  in  the 
Northern  states  it  is  necessary  to  return  to  heavy  winter 
wraps  after  a  season  of  high  temperature. 

In  the  early  autumn,  too,  when  cold,  damp  evenings 
and  nights  follow  hot,  sunny  days,  judicious  attention  to 
clothing  will  often  ward  off  the  intestinal  and  febrile 
diseases  prevalent  in  that  season.  It  is  frequently  wise 
to  change  the  underclothing  with  the  approach  of  night, 
putting  on  the  warm  wool  which  was  perhaps  intolerable 
at  midday.  Many  physicians  advise  as  a  safeguard  the 
wearing  of  a  broad  woolen  bandage  over  the  abdomen 
both  by  dav  and  bv  nio-ht. 

405.  The  Bodily  Heat  as  affected  by  Alcohol.  —  The  paralyz- 
ing effect  of  the  use  of  alcoholic  drinks,  upon  the  muscles 
in  the  walls  of  the  minute  blood  vessels,  has  been  men- 
tioned in  connection  with  the  muscles,  the  circulation, 
and  respiration.  It  should  be  referred  to  also  in  connec- 
tion with  the  subject  of  this  chapter. 

Because  alcohol  is  quickly  oxidized,  and  because  heat 
is  produced  in  the  process,  it  was  long  believed  to  be  of 
value  in  maintaining  the  heat  of  the  body.  A  different 
view  now  prevails  as  the  result  of  much  observation  and 
experiment.  Travelers  in  Arctic  regions  and  others 
exposed  to  intense  cold  agree  that  those  who  use  no 
alcohol  Avhatever  are  far  better  able  to  resist  the  cold 
than  are  those  who  indulge  in  it.  Physiologists  show  by 
careful  experiments  that  though  the  temperature  of  the 
body  rises  during  digestion  of  food,  it  is  lowered  for  some 
hours    when   alcohol   is  taken.     The   flush  which  is  felt 


272  UNCONSCIOUS   NERVOUS   OPERATIONS 

upon  the  skin  after  a  drink  of  wine  or  spirits  is  due  in 
part  to  an  increase  of  heat  in  the  body,  but  also  to  the 
paralyzing  effect  of  the  alcohol  upon  the  capillary  walls, 
allowing  them  to  dilate,  and  so  permitting  more  of  the 
warm  blood  of  the  interior  of  the  body  to  reach  the  sur- 
face. There  it  is  cooled  by  radiation,  and  the  general  tem- 
perature is  lowered. 


PART   IV 

THE   NERVOUS    SYSTEM 

All  our  previous  study  has  had  to  do,  directly  or  in- 
directly, with  the  nervous  system,  with  its  methods  of 
action,  its  instruments,  its  nutrition,  its  arrangement  and 
functions.  Now  we  are  to  examine  its  wonderful  and 
delicate  mechanism  more  in  detail,  to  inquire  further  into 
the  functions  which  the  various  parts  fulfill,  and  into  the 
manner  of  life  which  study  and  experience  have  shown  to 
be  most  conducive  to  the  preservation  of  the  most  impor- 
tant part  of  the  human  organism  in  health  and  efficiency. 

Even  the  limited  amount  of  knowledge  upon  this  great 
subject  which  is  within  the  reach  of  young  students  may 
be  made  valuable  in  enforcing  the  necessity  of  hygienic 
living,  and  also  as  a  basis  for  a  ready  appreciation  of  that 
larger  revelation  respecting  the  nervous  system  which 
science  will  from  time  to  time  unfold. 

In  presenting  this  fuller  description  of  the  nervous 
system  some  repetition  of  the  statements  given  in  Chap- 
ter HI  is  found  necessary. 


278 


Rg.  121;— The  nervous  system. 


274 


CHAPTER    XXI 

ANATOMICAL  DESCRIPTION 

406.  Composition  of  tlie  Nervous  System.  —  The  nervous 
system  is  made  up  of  nerve  centers^  nerves,  -^tl^ peripheral 
end  organs.  These,  though  really  constituting  a  single 
system  for  the  whole  of  man's  organism,  are  commonly 
described  in  two  separate  groups,  or  systems:  the  cerebro- 
spinal or  central  and  the  sympathetic  or  ganglionic. 

The  nerve  centers  are  the  brain  and  spinal  cord  (often 
called  the  cerebro-spinal  axis),  and  little  knots  of  nervous 
matter  found  in  different  parts  of  the  body,  along  the 
course  of  the  nerves,  called  ganglia.  All  nerve  fibers 
arise  in  the  nerve  centers. 

407.  Nervous  Elements.  —  AVe  have  learned  that  nerv- 
ous tissue  exists  in  two  forms :  gray  matter,  which  is 
almost  wholly  composed  of  nerve  cells,  and  luhite  matter^ 
which  is  almost  wholly  composed  of  nerve  fibers.  Nerve 
fibers  and  nerve  cells  constitute  the  nervous  elements. 

408.  The  Nerve  CeU.  — Xerve  cells  are  microscopic,  irreg- 
ular bits  of  protoplasm  like  other  cells.  Each  contains 
a  large  nucleus,  within  which  is  a  nucleolus,  and  usually 
each  cell  sends  off  one  or  more  fine  branches,  or  proc- 
esses (Fig.  122).  Sometimes  these  are  so  numerous 
as  to  give  the  cell  a  stellate  appearance.  Xerve  cells 
are  found   onlv  in  the    central   nervous   svstem,  in  the 


276  THE   NERVOUS   SYSTEM 

ganglia,  and   in   the   peripheral   terminations  of   certain 
nerve  fibers. 


Fig.  122.  — Nerve  cells  from  the  spinal  cord. 

A  nerve  cell  with  all  its  processes.  B  body  of  cell,  showing  nucleus  (iV) . 

409.  The  Axis  Cylinder,  or  Neuraxon.  —  One  of  the  proc- 
esses of  the  nerve  cell  —  and  as  a  rule  only  one  —  becomes 
what  is  called  the  axis  cylinder  of  a  nerve  JjJ)er.  It  is  a 
protoplasmic  thread  continuous  with  the  substance  of  the 
cell  and  usually  inclosed  within  a  sheath.  Axis  cylinder 
processes  give  off,  usually  at  right  angles,  fine  side 
branches  which  ramify  in  the  adjacent  nerve  substance 
(Fig.  123),  and  the  final  ending  of  the  axis  cylinder 
itself  is  in  many  minute  divisions.  Many  or  most  of  the 
nerve  cells  have  other  processes  which  do  not  become 
axis  cylinders,  but  end  in  fine  twiglike  divisions  in  the 
gray  matter  around  them. 

410.  The  Nerve  Fiber  (Fig.  124).— The  essential  part 
of  every  nerve  fiber  is  the  central  protoplasmic  core, 
which  is  always  the  axis  cylinder  process  of  a  nerve  cell. 
There  is  hence,  after  all,  only  one  fundamental  form  of 
nervous  matter,  viz.    the   protoplasm  of   the  nerve  cell, 


ANATOMICAL   DESCRIPTION 


277 


>>-^ 


Node  of 
Ranvier 


-Neurilemma 


The  central  thread  of  a  nerve  fiber  may  have  two  inclos- 
ing sheaths.  A  layer  of  white,  oily  matter  immediately 
surrounding  the  axis  cylinder  is  called 
the  medullary  sheathe  or 
sometimes  the  ivhite  suh- 
stmice  of  Schwann.  Out- 
side of  this  is  a  coat  of 
thin,  elastic  membrane 
called  the  pri77iitive  sheath^ 
or  neurilennna.  The  lat- 
ter covers  its  fiber  from 
end  to  end,  but  the  med- 
ullary sheath  is  broken 
at  frequent  intervals,  and 
between  the  breaks  the 
microscope  shows,  along 
the  course  of  the  axis  lit- 
tle nuclei  buried  in  min- 
ute masses  of  protoplasm. 
In  some  nerve  fibers 
the  medullary  sheath  is 
wanting,  leaving  only  the 
neurilemma  inclosing  the 
axis  cylinder.  These  are 
called  7ionmedullafed  nerve  fibers.  The  medullary  sheath 
is  brilliant,  shining  white  in  color,  and  gives  to  the  nerve 
its  characteristic  white  appearance.  The  nonmeduUated 
fibers,  therefore,  are  gray. 

Nerve  fibers  may  be  very  short  or  they  may  be  many 
feet  in  length.  Every  nerve  fiber  originates  in  a  nerve 
cell,  but  there  are  several  ways  in  which  it  may  end,  as 
has  already  been  shown. 

411.   A  Nerve  is  a  bundle  of  nerve  fibers  bound  together 


Xetiraocon 
'  or  Axis 
Cylinder 


Medullary 
Sheath 


Fig.  123.  — Nerve 
cells  (pyramidal ) 
of  the  cortex  of  the 
cerebrum. 

Ax  axis  cylinder  proc- 


Fig 


124.  — Por- 
tion of  a  me- 
duUated  nerve 
fiber. 


278 


THE   NERVOUS   SYSTEM 


by  a  little  connective  tissue  in  which  run  blood  vessels 
and  lymphatics,  the  whole  inclosed  in  a  sheath  called  the 
perineurium.  The  nerves  from  the  central  system  are 
composed  chiefly  of  meduUated  fibers,  with  which  are 
bound  up  a  few  nonmedullated  ones,  while  the  nerves 
of  the  sympathetic  system  are  made  up  almost  wholly  of 
the  gray  nonmedullated  fibers. 

412.  A  Ganglion  is  a  little  group  of  nerve  cells  forming 
a  nervous  center.  As  a  rule  (to  which  the  spinal  ganglia 
form  an  exception),  the  nerve  fibers  running  from  the  cen- 
tral system  to  a  ganglion  are  medullated,  while  those 
passing  from  the  ganglion  toward  the  periphery  are  non- 
medullated and  also  more  numerous. 

413.  Neuroglia.  —  The  fibers  and  cells  of  both  the  gray 
and  the  white  nervous  matter  are  supported  by  a  tissue 

called  neuroglia  (Fig.  125), 
which  is  composed  ©f  ex- 
tremely fine  fibers  and  cells. 
It  differs  chemically  and  in 
origin  from  the  connective 
tissues,  though  like  them  in 
function. 

414.  The  Nerve  Unit  or  Neu- 
ron. —  A  nerve  cell,  with  its 
two  sorts  of  processes,  con- 
stitutes a  nerve  unit,  or  neuron 
(Fig.  126).  That  is,  the  whole  nervous  system  is  built 
up  of  an  indefinite  but  enormous  number  of  these  units, 
supported  by  neuroglia  and  connective  tissue.  A  nerve 
cell  sends  off  one  process  (rarely  more),  which  is  pro- 
longed into  the  axis  cylinder,  or  neuraxon,  while  the 
numerous  other  branches,  called  dendrons  or  dendrites, 
almost  immediately  break  up  into  fine  twigs  or  brushlike 


Fig.  125.  — Neuroglia  cells. 


ANATOMICAL   DESCRIPTION 


279 


--Cell  Body 


Medulla 


Node  of  Ttanvier 


Neurilemma 


divisions.  The  dendrons  are  thought  by  some  to  be  con- 
cerned only  in  absorbing  nutriment  for  the  nerve  cell, 
while  other  investigators  believe  them 
to  have  also  some  part  to  play  in  the 
conduction  of  nerve  impulses.  Each 
neuron  is  anatomically  independent 
of  every  other.  There  is  no  continu- 
ous path  from  one  nerve  cell  to 
another.  The  fine  branches  from 
one  cell  mingle  and  interlace  with 
those  of  another  cell,  but  do  not 
become  connected  with  them  to  form 
a  continuous  channel,  any  more  than 
do  the  interlacing  branches  of  two 
trees  standing  side  by  side  form  com- 
municating channels  for  the  passage 
of  the  sap  of  one  to  the  other. 
Nervous  influences  do  indeed  pass 
from  one  nerve  unit  to  another  by 
some  method  not  yet  understood, 
perhaps  by  a  process  similar  to  that 
of  electrical  induction;  but  the  old 
idea  of  an  uninterrupted  channel  for 
the  passage  of  a  nervous  impulse  from  center  to  periphery 
and  from  periphery  to  center  is  now  abandoned.  There 
may  be  several  breaks  in  the  course  of  transmission,  as 
there  often  are  in  the  sending  of  a  telegraphic  message. 
The  two  sorts  of  branches  also  preserve  their  identity 
from  beginning  to  end  of  each  minutest  filament.  There 
is  no  real  network  of  nerve  fibers  in  the  nervous  system. 

415.  The  Spinal  Cord  (Fig.  18,  p.  28)  is  a  column  of 
nervous  matter  from  fifteen  to  eighteen  inches  in  length 
in  the  adult,  from  the  foramen  magnum^  through  which 


Fig.  126.  —Diagram  of  a 
neuron  or  nerve  unit. 


280 


THE  NERVOUS   SYSTEM 


Posterior  Fissure 


its  fibers  pass  into  the  brain,  to  the  fine  gray  filament 
which  forms  its  termination  in  tlie  lumbar  vertebrae. 
A  cross  section  shows  it  to  be  composed  of  white  fibrous 
matter,  surrounding  a  central  core  of  gray  cellular  matter 
(Fig.  127).  The  gray  matter  presents  in  section  a 
rough  outline  of  the  letter  H.  In  the  middle  of  the 
cross  bar,  or  isthmus,  connecting  the  two  sides  of  the  let- 
ter, is  a  minute  chan- 
nel which  extends  the 
whole  length  of  the 
cord  and  on  into 
the  brain.  The  ends 
of  the  letter  H  which 
point  forward  are 
club-shaped  and  are 
known  as  the  anterior 
horns  of  the  gray  mat- 
ter of  the  cord,  while 
those  pointing  back- 
ward are  pointed  and 
are  called  posterior 
horns.  The  last  cut 
through  the  white 
matter  nearly  to  the 
surface  of  the  cord. 
The  white  matter  of  the  cord  is  composed  of  meduUated 
fibers,  running  for  the  most  part  longitudinally,  together 
with  fibrous  connective  tissue  and  neuroglia.  These  fibers 
are  arranged  in  several  different  strands,  or  bundles,  and 
their  areas  have  been  carefully  mapped  out  and  named. 
In  each  half  of  the  cord  is  an  anterior,  a  lateral,  and  a  pos- 
terior column,  named  from  their  positions  and  separated 
from  one  another  by  the  shallow  depressions  seen  in  the 


Anterior  Fissure 

Fig.  127.  — Diagram  of  a  cross  section  of 
the  spinal  cord,  showing  the  divisions 
of  the  white  and  gray  matter. 

The  right  half  shows  the  threefold  division 
of  the  white  matter  commonly  described  ;  the 
left  half  shows  the  physiological  divisions  as 
they  are  at  present  understood. 


ANATOMICAL   DESCRIPTION 


281 


surface  of  the  cord.  The  gray  matter  consists  largely  of 
nerve  cells  with  many  branching  processes,  but  there  are 
also  many  delicate  nerve  fibers,  together  with  the  support- 
ing neuroglia.  The  cord  is  divided  into  symmetrical 
halves  by  fissures  before  and  behind,  the  posterior  fissure 
being  the  deeper,  and  the  anterior  wider  and  more 
distinct.  Neither  of  the  fissures  cuts  quite  through  the 
white  matter  to  the  gray  in  the  center. 

416.   Spinal  Nerves.  —  From  the  grooves  nearest  the  ante- 
rior fissure  spring,  by  many  fine  rootlets,  the  anterior  roots 


Fig.  128.  —Diagrammatic  cross  section  of  the  spinal  cord,  showing  the 
origin  and  the  chief  divisions  of  a  spinal  nerve. 

A  anterior  column  of  wliite  matter. 
I)  posterior  branch  of  nerve  trunk. 
Ga  ganglion  on  the  posterior  root  of  the  nerve,  containing  the  cells  from  which 

arise  most  of  the  fibers  of  the  sensory  root  {S) . 
Gr  gray  matter  of  the  cord. 
L     lateral  column  of  white  matter. 
M    anterior  or  motor  root  of  the  nerve. 
Mc  motor  cells  from  which  arise  the  motor  nerve  fibers. 
N    main  trunk  of  the  nerve. 
P     posterior  column  of  white  matter. 
5     posterior  or  sensory  root  of  the  nerve. 
Sij  ganglion  of  the  sympathetic  system  which  communicates  with  the  spinal 

nerve. 
V    anterior  branch  of  nerve  trunk. 


of  the  spinal  nerves,  while  the  posterior  roots  of  the  same 
nerves  appear  to  rise  near  the  other  groove  on  the  same 
side  (Fig.  128).     The  two  roots  soon  unite; — but  before 


282  THE   NERVOUS   SYSTEM 

their  union  the  posterior  root  ]3asses  through  a  little  knot 
of  gray  matter,  called  the  spinal  ganglion. 

The  cells  of  the  anterior  horn  of  the  gray  matter  of  the 
cord  are  large  and  branching,  and  each  cell  sends  off  an 
axis  cylinder  process  which  passes  out  in  an  anterior  nerve 
root.  Careful  experiments  have  shown  that  the  fibers  in 
the  posterior  nerve  roots  of  spinal  nerves  arise  in  the  spi- 
nal ganglion.  The  nerve  fibers  which  form  this  posterior 
root  are  axis  cylinder  j^rocesses  from  nerve  cells  in  the 
spinal  ganglion.  As  they  pass  out  from  the  ganglion  each 
divides  into  two  branches,  one  of  which  goes  to  form  a 
sensory  nerve  fiber  in  the  spinal  nerve.  The  other  turns 
back  and  enters  the  spinal  cord,  where  it  again  divides, 
its  fibers  ending  variously.  The  main  division  of  the 
branch  from  the  ganglion  passes  up  to  the  brain,  giving 
off  fine  collaterals  which  end,  by  "  arborizing  "  (as  the 
brushlike  ending  is  called),  round  nerve  cells  at  different 
levels  in  the  cord.  In  general,  the  posterior  root  fibers 
travel  upward  mainly  in  the  white  columns  of  tlie  cord, 
while  only  a  few  fibers  enter  the  gray  matter  of  the  cord. 

417.  Thirty-one  pairs  of  spinal  nerves  issue  from  the 
spinal  cord  (Fig.  18,  p.  28),  each  nerve  containing 
both  afferent,  or  sensory,  nerve  fibers  from  the  posterior 
root,  and  efferent,  or  motor,  fibers  from  the  anterior  root. 
These  fibers  remain  distinct  from  each  other  for  their 
whole  length.  The  spinal  nerves  are  distributed  by  many 
branches  to  the  skin  and  skeletal  muscles;  they  also  form 
connection,  by  what  are  called  communicating  branches, 
with  the  ganglia  of  the  sympathetic  system  (Figs.  128  and 
136),  and  are  afterward  distributed  to  the  viscera.  The 
whole  of  the  sympathetic  system  may  be  regarded  as 
simply  the  development  of  these  communicating  branches 
from  certain  spinal  nerves. 


ANATOMICAL   DESCRIPTION  283 

418.  Plexuses.  —  We  have  already  seen  that  in  many 
regions  of  the  body,  especially  about  the  neck,  loins,  and 
pelvis,  adjacent  nerves  interlace  to  form  a  network,  or 
nervous  plexus.  Nerves  passing  outward  from  a  plexus 
contain  libers  from  several  different  nerves,  and  the  parts 
to  Avhich  these  nerves  are  distributed  are  thus  sometimes 
brought  into  connection  with  a  considerable  part  of  the 
central  nervous  system.  The  nerves  which  supply  the 
limbs,  where  very  complex  muscular  movements  are  re- 
quired, and  where  nervous  coordination  of  those  move- 
ments is  necessary,  come  from  large  plexuses  where  fibers 
from  many  nerves  are  intermingled.  (It  should  be  remem- 
bered that  the  term  '•  network  "  is  here  used  subject  to  the 
limitation  given  above  [p.  279]  and  does  not  imply  more 
than  is  there  stated.) 

By  means  of  the  spinal  nerves  nearly  all  the  nervous 
impulses  from  the  trunk  and  limbs  pass  through  the  spi- 
nal cord  to  the  brain. 

419.  Membranes  of  the  Brain  and  Spinal  Cord.  —  Three 
membranes  inclose  the  brain  and  spinal  cord.  The  dura 
mater  is  a  tough,  white  fibrous  and  elastic  membrane  lin- 
ing the  bony  cavity  of  the  skull  which  contains  the  brain, 
and  the  vertebral  canal  in  which  lies  the  spinal  cord.  It 
also  lies  in  folds  between  the  divisions  of  the  brain. 

The  arachnoid  is  a  thin  membrane  of  loose  connective 
tissue,  forming  a  sort  of  closed  sac  (like  the  pericardium), 
which  secretes  a  serous  fluid.  It  lies  betw^een  the  dura 
mater  and  the  pia  mater. 

The  pia  mater  is  an  extremely  delicate,  highly  vascular 
membrane  (that  is,  having  many  blood  vessels),  closely 
investing  the  nervous  matter  of  the  spinal  cord  and  the 
brain.  It  follows  all  the  curves  and  convolutions  of  the 
brain,  and  carries  to  all  its  parts  and  to  the  spinal  cord 


284 


THE   NERVOUS  SYSTEM 


numerous  blood  vessels  which  assist  in  their  nutrition. 
The  three  membranes  are  sometimes  called  the  cerebro- 
spinal meninges,  and  the  serious  disease  called  cerehro- 
spinal  meningitis  is  due  to  inflammation  of  these  lining 
membranes. 


Corpus  Callosum 


Foramen  of  Monro 

\   Third  Ventricle 

\  Pineal  Body 

\  1  Cerebrum 


Fornix 


Optic  Chiasma 

Pituitary  Body     / 

Oculomotor  Nerve      / 

Pons  Varolii     /        / 

Aqueduct       /       / 
Medulla  Oblongata     / 
Fourth  Ventricle 


'--Corpora 
Quadngemina 

Cerebellum 


Spinal  Cord 


Fig.  129.— The  right  half  of  a  vertical  median  section  of  the  brain. 


420.   The  Brain  (Figs.  129,  130,  131,  and  134).— The 

division  of  the  brain  into  five  principal  parts  is  derived 
from  the  manner  of  the  development  of  those  parts  from 
certain  primary  divisions  of  the  embryo.  Those  parts 
are  :  (1)  the  cerebrum,  with  its  two  hemispheres  ;  (2)  the 
optic  thalami  ;  (3)  the  corpora  qiiadrigemina,  or  optic  lobes^ 
with  the  crura  cerebri ;  (4)  the  cerebellum  and  pons  Varolii; 


ANATOMICAL   DESCRIPTION 


285 


aud  filially  (5)  the  meduUa  oblongata.     More  minute  divi- 
sions might  be  and  often  are  given,  but  these  are  sufficient 

for  the  present  purpose. 


Corpus  Callosum 

\ 

--Corpus  Striatum 
Font  (X 


-Optic  Thalamus 
Pineal  Body 
-Corpora  Quadrigeinina 
Trochlear  Xerve 


Fig.  130. —  Brain  viewed  from  above,  with  the  cerebellum  and  a  large 
part  of  the  cerebrum  removed,  exposing  the  structures  hidden  by 
the  cerebrum. 

1.  2.  3  CUT  surfaces  of  the  peduncles  of  the  cerebelhim. 

421.  The  Cerebrum  (Fig.  131). — More  than  two  thirds 
of  the  whole  weight  of  the  brain  belongs  to  the  two  hemi- 
spheres of  the  cerebrum.  Its  surface  of  gray  matter, 
called  the  cortex,  presents  a  characteristic  folded  appear- 
ance, the  convokitions  being  separated  by  fissures.  The 
deeper  fissures  divide  each  hemisphere  into  five  lobes, 
called,  from  their  locations  in  the  cranium,  the  frontal^ 
parietal,  temporal  occipital,  and  central  lobes,  the  last  being 
also  called  the  insula  or  island  of  Reil.  The  insula  is  not 
mact's  phys.  — 18 


286 


THE   NERA^OUS   SYSTEM 


visible  from  the  surface,  but  lies  deep  within  the  Sylvian 
fissure^  which  divides  the  frontal  from  the  temporal  lobe, 
and  is  concealed  by  the  convolutions  of  the  upper  lobes 


Fissure  of 
Rolando 


Parietal  Lobe 


Oocipito-parietal 
,     Fissure 


Frontal  Lobe 


tal  Lobe 
Sylvian  Fibsure 
Tempo)  al  Lobe 


Fig.  131.— Side  view  of  the  left  cerebral  hemisphere. 


(Fig.  132).  Other  principal  fissures  are  the  deep  lon- 
gitudinal one  separating  the  hemispheres  ;  the  fissure  of 
Rolando^    Avhich   lies   between    the   frontal    and    parietal 

lobes  ;  and  the  occipito- 
parietal fissure^  separat- 
ing the  parietal  from 
the  occipital  lobe.  A 
broad  band  of  white 
nerve  fibers,  the  corpus 
callosum^  connects  the 
two  hemispheres  (Fig. 
129).  In  the  base  of 
each  frontal  lobe  is  a 
bulbous  expansion  of  gray  and  white  matter  connected 
by  a  stalk,  or  peduncle,  called  the  olfactory  tract,  with  the 
mass  of   the  hemisphere.     These  are  the  olfactory  bulbs, 


Fig.  132.  —Side  view  of  brain  with  tem- 
poral lobe  cut  away  so  as  to  expose 
the  underlying  insula. 


ANATOMICAL  DESCRIPTION  287 

with  which  are  connected  the  olfactory  nerves  (Fig.  134). 
They  are  direct  outgrowths  of  the  brain  substance.  Lying 
partly  in  the  lateral  ventricles  (§  42G)  and  j^artly  embedded 
in  white  substance  of  the  hemispheres,  are  the  pear-shaped 
corpora  striata  (Fig.  130),  composed  of  white  and  gray 
matter.      They  are  ganglia  on  the  path  of  motor  nerves. 

422.  The  Optic  Thalami  are  masses  of  gray  matter  in  the 
base  of  the  cerebrum  (Fig.  130),  and  are  closely  con- 
nected with  the  corpora  striata,  which  belong  to  the  cere- 
brum. These  two  pairs  of  gray  bodies  are  often  called  the 
hasal  ganglia.  From  them  nerve  fibers  radiate  into  the 
convolutions  of  the  cerebral  hemispheres.  The  optic  thai- 
ami  are  ganglia  on  the  path  of  sensory  nerves  ;  the  corpora 
striata  belong  to  the  motor  tract. 

423.  The  Corpora  Quadrigemina,  or  Optic  Lobes,  and  the 
Crura  Cerebri.  —  The  corpora  quadrigemina,  oy  optic  lohes^  lie 
behind  and  between  the  optic  thalami  (Figs.  129  and  130). 
They  are  masses  of  gray  matter,  or  rather  a  single  body 
divided  by  shallow  fissures  into  four  hemispherical  parts. 
The  optic  tracts  arise  superficiall}^  from  their  surfaces. 
The  optic  lobes  rest  upon  the  hinder  face  of  the  crura 
cerebri.  These  latter  are  bundles  of  nerve  fibers  forming 
peduncles,  or  stalks,  which  connect  the  cerebrum  with 
other  parts   of  the  brain. 

424.  The  Cerebellum  and  Pons  Varolii  (Figs.  129  and 
131). — The  cerehellum  is  composed  of  gray  and  white 
matter,  and  lies  in  two  hemispheres  across  the  back  of  the 
cerebro-spinal  axis.  The  hemispheres  are  connected  by 
bands  of  white  matter,  called  peduncles,  with  each  other 
and  with  other  parts  of  the  brain.  The  white  matter  of 
the  cerebellum  is  arranged  on  each  side  in  a  central  trunk, 
which  divides  into  many  branches,  around  which  the  gray 
matter  is  placed,  the  whole  forming  what  is  called,  from 


288  THE   NERVOUS   SYSTEM 

its  likeness  to  a  branching  tree,  "the  tree  of  life."  The 
gray  surface  is  arranged  in  parallel  ridges,  or  laminated 
folds,  differing  from  the  irregular  convolutions  of  the 
cerebrum. 

The  pons  Varolii  also  contains  white  and  gray  matter. 
In  it  white  fibers  pass  upward  to  connect  the  medulla  ob- 
longata with  other  parts  of  the  brain.  It  contains,  also, 
the  strands  of  white  matter  which  form  the  middle 
peduncle  of  the  cerebellum.  The  pons  is,  therefore,  as  its 
name  implies,  the  passage,  or  bridge,  by  means  of  which 
connection  is  made  between  all  parts  of  the  nervous 
system. 

425.   The  Medulla  Oblongata,  or  Spinal  Bulb,  is  the  enlarged 
upper  portion   of   the   spinal    cord  contained   within  the 
cavity  of  the  cranium  (Figs.  129,  130,  and  134).     It  is 
conical  in  shape,  about  one  inch  in  thickness  at  its  broad- 
est part,  and  about  one  inch  and  a  quarter  in  length,  and 
consists  of  two  symmetrical  halves.     On  the  forward,  or 
anterior,  surface  is  seen  a  deep  groove,  which  is  a  con- 
tinuation of  the  anterior  fissure  of  the  cord.     A  similar 
but   more    shallow    fissure   forms    the    posterior   division 
between  the  halves.     Just  as  the  cord  begins  to  expand 
into  the  medulla,  many  of  the  fibers  which  compose  the 
lateral  columns   of  the  cord  cross  from  one  side  to  the 
other.      These   bundles    of    white   fibers    are    called,   in 
the  medulla,  the  pyramids,  and  their   crossing  is   called 
the    decussation    of  the  pyramids.       Other  fibers   of   the 
pyramidal  tracts  cross  lower  down  at  different  levels  in 
the  cord.     In  general,  a  rearrangement  of  the  fibers  of  the 
cord  takes  place  in  the  medulla.     What  it  is  especially 
important  to  notice  is  that  each  tract  of  fibers  in  the  cord 
has  connection  through  the  medulla  with  the  centers  in 
both  the  cerebellum  and  the  cerebrum. 


ANATOMICAL   DESCRIPTION 


289 


The  gray  matter  of  the  medulla  oblongata  is  partly 
continuous  with  that  of  the  cord,  but  is  partly  broken  up 
into  independent  groups  of  cells,  or  nuclei,  which  are  the 
deep  origins  of  most  of  the  cranial  nerves. 

426.  The  Ventricles  of  the  Brain,  and  the  Cerebro-spinal 
Fluid.  —  The  ventricles  are  irregular  cavities  in  the  brain, 
communicating  with  one  another  and  continuous  with  the 
canal  of  the  spinal  cord  (Fig.  133).  The  lateral  ventricles 
lie  one  in  each  hemisphere  of  the 

cerebrum.  They  open  into  the 
third  ventricle^  which  is  in  the  mid- 
dle line.  A  narrow  canal,  called 
the  aqueduct  of  Si/lvius,  connects 
the  third  with  the  fourth  ventricle, 
of  which  the  back  of  the  pons  and 
the  medulla  oblongata  form  the 
floor,  while  the  overhanging  cere- 
bellum forms  part  of  its  roof.  A 
small  opening  in  the  pia  mater, 
which  completes  the  roof  of  the 
fourth  ventricle,  makes  connec- 
tion between  these  interior  cavities  and  the  external  sur- 
face of  brain  and  cord,  so  that  the  fluid  which  fills  the 
space  beneath  the  arachnoid  is  continuous  with  that  in 
the  inside. 

The  cerebrospinal  fluid  is  a  thin,  watery  substance  which 
bathes  the  external  surfaces  of  the  brain  and  spinal  cord, 
and  fills  the  ventricles  and  the  spinal  canal. 

427.  The  Cranial,  or  Cerebral,  Nerves  (Figs.  134  and  135). 
—  Of  the  twelve  pairs  of  nerves  issuing  from  the  brain, 
ten  have  their  deep  origins  in  the  floor  of  the  fourth  ven- 
tricle or  in  adjacent  gray  matter.  Each  cranial  nerve  is 
said  to  have  a  deep  origin,  which  is  that  portion  of  gray 


Fig.  133.  — Cast  of  brain 
cavities. 


290 


THE   NERVOUS   SYSTEM 


matter  where  its  fibers  rise  from  nerve  cells,  and  a  super- 
ficial origin^  which  is  the  region  of  the  brain  surface  from 
which  the  nerve,  as  a  nerve,  departs  upon  its  mission. 

1.  The  first  pair  of  cranial  nerves  are  the  olfactory 
nerves,  distributed  directly  and  wholly  to  the  organ  of 
smell,  and  sensory  in  function. 


Olfactory  Bulb 

{^to  which  is  attached 
the  Olfactory  Nerve) 

Pituitary  Body — _ 

Optic  Nerve — 

Optic  Chiasma 

Oculotnotor  Nerve — _ 
Trochlear  Nerve — _ 
Trigeminal  Nerve- ^_ 
Pons  Varolii- ~^ 
Abducens  Nerve-  _ 
Facial  Nerve — 
Auditory  Nerve- ^ 
Glossopharyngeal  Nerve  __ 

Vagus  Nerve . 

Spinal  accessory  Nerve 1 

Hypoglossal  Nerve- - 

Medulla  Oblongata 

First  Spinal  Nerve 

Cerebellum 

Spinal  Cord 

Second  Spinal  Nerve  ^ 


rig.  134.  — Ventral  (anteriorj  surface  of  the  brain. 


2.  The  optic  nerves  go  to  the  organs  of  sight.  From 
their  deep  origins  to  the  point  where  a  part  of  their 
fibers  cross  they  are  called  the  optic  tracts.  They  are 
sensory. 

3.  The  oculomotor  nerve  supplies  all  the  muscles  of  the 
eyeball  except  the  superior  oblique  and  external  rectus, 


ANATOMICAL   DESCRIPTION 


291 


and  communicates  with  a  nerve  plexus  of  the  sympathetic 
system. 

4.  The  trochlear^  the  smallest  of  the  cranial  nerves,  is 
motor.  It  supplies  the  superior  oblique  muscle  of  the  eye, 
and  communicates  v^^ith  the  same  plexus  as  does  the  third 
nerve. 

5.  The  trigeminal^ 
the  largest  cranial 
nerve,  is  mixed  in 
function.  Its  motor 
division  goes  to  the 
muscles  of  mastica- 
tion. The  larger 
division  is  the  great 
sensory  nerve  of  the 
face  and  head. 

6.  The  abducens 
supplies  the  external 
rectus  muscle  of  the 
eyeball  as  its  motor 
nerve. 

7.  The  facial  is 
the  great  motor  nerve 
of  the  muscles  of  the  face.  One  of  its  branches,  the 
chorda  tympanic  passes  across  the  tympanum  and  joins  the 
lingual  branch  of  the  fifth  nerve.     It  is  purely  motor. 

8.  The  auditory^  a  sensory  nerve,  leaves  the  surface  of 
the  brain  in  tAvo  roots  :  one,  the  cochlear  branchy  is  the 
auditory  nerve  proper,  and  goes  to  the  cochlea  ;  the  ves- 
tibular branch  ends  in  the  semicircular  canals,  the  utricle, 
and  the  saccule. 

9.  The  glossopharyngeal,  after  communicating  with 
several   neighboring   nerves  and  ganglia,   separates   into 


\it  and  2nd 

Spinal  Nerves 


Fig.  135. 


Diagram  of  the  distribution  of 
the  cranial  nerves. 


292  THE   NERVOUS   SYSTEM 

two  main  divisions.  One  goes  to  the  pharynx,  the  Eus- 
tachian tube,  the  palate,  and  the  tonsils,  as  a  motor  nerve 
chiefly.  The  other  is  the  nerve  of  taste  for  the  back  part 
of  the  tongue. 

10.  The  vagus^  or  pneumo gastric^  is  the  wandering  nerve. 
It  is  longer  and  has  a  more  complicated  distribution  than 
any  other  cranial  nerve.  It  sends  branches  to  pharynx, 
larynx,  esophagus,  stomach,  intestines,  lungs,  heart,  liver, 
and  spleen.     It  is  both  sensory  and  motor. 

11.  The  spinal  accessory^  a  purely  motor  nerve,  con- 
tains fibers  from  a  nervous  center  in  the  walls  of  the 
fourth  ventricle,  and  from  the  anterior  horns  of  the  spinal 
cord.  The  latter  fibers  pass  up  into  the  cranium  and  join 
the  cerebral  fibers  of  this  nerve  just  before  it  passes  out 
of  the  skull.  The  nerve  has  two  branches,  one  of  which 
joins  the  vagus,  to  which  it  supplies  motor  fibers  and 
inhibitory  fibers  for  the  heart,  while  the  other  supplies 
certain  muscles  of  the  shoulder  blade  and  neck. 

12.  The  hypoglossal  is  connected  with  the  vagus,  with 
a  ganglion  of  the  sympathetic  system,  and  with  some  of 
the  upper  spinal  nerves.  It  is  the  motor  nerve  for  the 
muscles  connected  with  the  hyoid  bone  and  the  tongue, 
and  sends  a  branch  to  some  muscles  of  the  neck  and  chest. 
It  also  contains  vasomotor  filaments. 

428.  The  Nervous  End  Organs  have  been  described  in 
previous  chapters,  and  are  mentioned  here  to  complete 
the  anatomical  view  of  the  nervous  system.  They  are  in 
man  of  three  classes,  viz.  end  plates  of  different  forms 
found  in  the  muscles,  organs  of  special  sensation,  and 
secreting  cells  found  in  the  various  glands. 

429.  The  Sympathetic  System  (Fig.  136). — What  is 
commonly  called  the  sympathetic  or  gayiglionic  system  con- 
sists of  a  double  chain  of  ganglia,  twenty-four  upon  each 


Cervical  Spinafr'' 
Xervea 


Dorsal  Spinal  , 
Nerves       < 


Lumbar  Spina? 
Xerre-s 


Sacral 
SpiiiaU-— 
Nerves  ""^^  / 


Fig.  136— Diagram  of  the  sympathetic  nervous  system. 
G  ganglion  chain.  Co  coccygeal  spinal  nerve. 


294 


THE   NERVOUS   SYSTEM 


■^tSolar  Plexus 


side,  lying  along  the  whole  length  of  the  spine.  They 
are  connected  by  white  fibers  with  the  spinal  cord,  with 
one  another  by  gray  or  nonmedullated  fibers,  and  with 
the  spinal  nerves  by  both  white  and  gray  fibers.  At  their 
upper  extremities,  and  in  other  situations  also,  the  great 
sympathetic  nerve  trunks  come  into  connection  with  all 
the  cranial  nerves  except  the  olfactory,  auditory,  and 
optic. 

The   gray  fibers  issuing  from  the  ganglia  are  usually 
too  minute  to  be  visible  to  the  naked  eye,  and  they  are 

much  more  numerous  than 
those  received  by  the  ganglia 
from  the  central  system. 
Most  of  these  gray  fibers 
seem  to  convey  efferent  im- 
pulses to  the  tissues,  though 
some  are  afferent,  carrying 
impulses  from  the  visicera  to 
the  central  system.  But  a 
certain  number  of  the  fibers 
from  the  main  sympathetic 
chain  turn  back  from  the 
ganglion  toward  the  center, 
some  to  reach  the  membranes 
of  the  spinal  cord,  some  to 
follow  the  course  of  the  prin- 
cipal branch  of  the  spinal 
nerve  which  is  distributed  to 
the  skeletal  muscles  and  the 
skin.  Nervous  connection  is 
thus  established  between  all  these  various  parts.  In  their 
distribution  the  sympathetic  nerves  follow  closely  the 
course    of    the   blood   vessels,   around   which  they   form 


L.  Sympathetic 

Chain 
B.  Sympathetic 

Chain 


Fig.  137— The   solar    and   hypo 
gastric  sympathetic  plexuses. 


ANATOMICAL  DESCRIPTION  295 

plexuses,  fibers  from  which  accompany  the  blood  vessels 
throughout  the  body,  penetrating  to  all  parts  of  the  various 
organs.  In  the  abdomen  is  found  also  a  great  plexus  of 
nerve  fiber  called  the  wlar  plexus,  because  smaller  plexuses 
radiate  from  it  like  rays  of  liglit  from  the  sun  (Fig.  137). 
From  the  solar  plexus  nerve  filaments  are  distributed  to  all 
the  abdominal  organs. 

Demonstration 

125.  Dissection  of  the  Brain. —  The  specimens  used  in  Ex.  6  (p.  33) 
should  now  be  studied  more  in  detail.  The  brain  should  be  divided 
into  two  symmetrical  halves,  and  the  longitudinal  median  section,  thus 
exposed,  should  be  compared  with  Fig.  129.  In  this  way  all  the  parts 
of  special  importance  can  be  identified.  Care  should  be  taken  that 
the  pupil  makes  this  careful  detailed  comparison  and  identification. 
Slice  away  the  dorsal  (upper)  surface  of  the  cerel)rum  till  a  cavity, 
the  lateral  ventricle^  is  reached.  By  carefully  removing  the  roof  of 
this  cavity  the  latter  is  seen  to  extend  forward  and  downward  as  the 
anterior  cornu,  and  downward  and  backward  as  the  descending  cornu. 
The  corpus  striatum  is  an  oval  mass  projecting  into  the  cavity  of  the 
anterior  cornu.  The  hippocampus  is  an  oval  projection  forming  the  floor 
of  the  posterior  part  of  the  lateral  ventricle,  including  the  descending 
cornu.  Between  the  corpus  striatum  and  the  hippocampus  extends 
a  fibrous  band,  the  descending  pillars  of  the  fornix.  This  band  can 
be  traced  to  the  middle  line  and  seen  to  be  a  part  of  the  fornix 
cut  in  the  median  section.  Cut  away  the  hippocampus  and  the  band 
of  the  fornix;  the  optic  thalamus  is  exposed  (see  Fig.  130).  Posterior 
to  the  thalamus  are  the  two  corpora  quadrigemina  of  that  half  of  the 
brain.  Between  the  descending  pillars  of  the  fornix  and  the  optic 
thalamus  is  a  narrow  opening,  the  foramen  of  Munro,  which  commu- 
nicates with  the  third  ventricle  and  through  the  latter  with  its  fellow 
of  the  opposite  half  of  the  brain.  By  this  means  the  two  lateral  ven- 
tricles communicate  with  each  other  and  with  the  other  cavities  of 
the  brain. 

The  cerebellum  will  be  found  on  close  examination  to  be  attached 
to  the  rest  of  the  brain  by  three  pairs  of  fibrous  bands.     One  pair, 


296  THE   NERVOUS   SYSTEM 

the  superior  peduncles,  connect  the  cerebellum  with  the  corpora  quad- 
rigemina;  a  second,  the  middle  peduncles,  form  the  lateral  extensions 
of  the  pons  Varolii ;  the  third,  inferior  peduncles,  connect  with  the 
spinal  cord.  By  severing  the  connections  of  the  cerebellum  the  cut 
ends  of  these  peduncles  may  be  seen.  Other  parts  of  the  brain  can 
be  identified  by  comparing  with  the  illustrations  of  the  human  brain 
given  in  the  general  text. 

If  the  brain  has  been  carefully  removed  from  the  skull,  the  twelve 
pairs  of  cranial  nerves  can  be  identified  by  careful  dissection  and  by 
comparison  with  the  figures  of  the  human  brain. 


CHAPTER   XXII 

FUNCTIONS   OF   THE   NERVOUS   SYSTEM 

430.  In  a  broad  sense,  the  functions  of  the  nervous  sys- 
tem may  be  said  to  be  to  bring  its  possessor  into  due  rela- 
tion with  the  universe  of  which  he  is  a  part,  and  to  enable 
him  to  live  that  life  to  which  his  organism  is  adapted ;  to 
supply  channels  of  communication  between  all  parts  of 
the  body;  to  supervise,  direct,  and  control  all  the  con- 
scious and  unconscious  activities  of  the  organism.  More 
specifically  they  are,  in  the  case  of  man,  sensations,  gen- 
eral and  special ;  regulation  of  all  motion ;  control  of  all 
vital  processes ;  and  the  manifestation  of  mental  opera- 
tions,—  thought,  will,  and  emotion. 

431.  Sources  of  Knowledge.  —  We  have  two  sources  of 
information  respecting  the  action  of  the  various  parts  of 
the  nervous  system.  There  is,  first,  observation  upon 
human  subjects.  Obviously  few  experiments  can  be  made 
upon  man  himself,  but  by  careful  study  of  man  in  health 
and  of  symptoms  shown  in  diseases  which  affect  the  brain 
and  nerves,  much  has  been  discovered.  The  second  source 
of  knowledge  is  from  experiments  upon  animals.  Electri- 
cal stimulation  acts  upon  the  nerves  much  as  does  the 
natural  nervous  stimulus,  and  by  its  use  in  the  physiologi- 
cal laboratory,  and  by  the  destruction  of  one  part  or  another 
of  the  nervous  system  of  an  animal,  the  paths  of  transmis- 
sion of  impulses  and  the  functions  of  the  different  parts 

297 


298  THE   NERVOUS   SYSTEM 

have  been  gradually  made  out.  While  our  knowledge  of 
the  functions  of  the  nervous  system  has  thus  been  greatly 
extended,  especially  during  recent  years,  it  is  probable 
that  a  much  larger  field  still  remains  only  partly  explored, 
and  there  is  reason  to  expect  that  a  much  more  accurate 
and  definite  acquaintance  with  this  most  important  portion 
of  the  human  organism  will  soon  become  possible. 

432.  Functions  of  the  Nerves.  —  The  nerves  are  the  tele- 
graph wires  of  the  system.  They  transmit  impulses 
from  all  parts  of  the  body  to  the  central  nervous  system 
and  from  the  central  system  to  all  parts  of  the  body. 
Individual  nerve  fibers  transmit  impulses  in  only  one 
direction. 

433.  Afferent  and  Efferent  Nerves.  —  Nerves  or  nerve 
fibers  which  carry  nervous  impulses  to  the  centers  are 
afferent ;  those  which  carry  impulses  from  the  centers  are 
efferent.  The  first  are  generally  called  sensory ;  but  im- 
pulses which  do  not  result  in  sensation,  that  is,  which  do 
not  affect  consciousness,  may  be  conveyed  by  afferent 
nerves.  The  spinal  cord  may  be  cut  or  injured  so  that 
its  lower  portion  and  the  nerves  issuing  from  it  have  no 
connection  with  the  brain.  Still  if  the  foot  is  pricked  or 
tickled,  the  afferent  nerves  carry  the  impulse  to  the  cord, 
efferent  nerves  bring  back  a  motor  impulse,  and  the  foot 
is  drawn  back,  all  without  conscious  sensation. 

434.  Classification  of  Nerves.  —  Afferent  nerves  have  been 
classed  in  two  groups. 

1.  Nerves  of  special  sense,  viz.  of  sight,  hearing,  touch, 
taste,  and  smell. 

2.  Nerves  of  general  sensibility.  These  convey  to  the 
brain  those  vague,  indescribable  feelings  of  comfort  and 
general  well-being,  or  of  discomfort,  languor,  and  weari- 
ness, which  come  from  the  interior  of  the  body. 


FUNCTIONS   OF   THE   NERVOUS   SYSTEM  299 

Excessive  stimulation  of  any  of  these  nerves  results  in 
j>ain. 

435.  Eferent  Nerves  carry  impulses  of  many  kinds  be- 
sides those  of  motion.  Five  classes  of  these  nerves  in  the 
human  system  have  been  described:  — 

1.  3Iotor  nerves,  distributed  to  the  voluntary  and  in- 
voluntary muscles,  and  carrying  impulses  resulting  in 
movement. 

2.  Accelerator  nerves,  which  increase  the  rate  of  rhyth- 
mical action,  as  in  the  heart. 

3.  Inhihitory  nerves,  which  retard  or  wholly  check 
rhythmical  action,  as  in  certain  nerve  fibers  of  the  heart. 

4.  Secretory  nerves,  which  convey  from  the  central  sys- 
tem to  the  glands  impulses  resulting  in  the  secretion  of 
their  special  products. 

5.  Trophic  (from  a  Greek  word  meaning  ''  nursing '") 
nerves,  which  control  the  nutrition  of  the  parts  to  which 
they  go. 

Still  other  nerves  exist  which  can  be  classed  neither  as 
afferent  nor  efferent.  They  are  those  which  connect  dif- 
ferent parts  of  the  brain  and  cord  with  one  another,  and 
in  general  form  lines  of  communication  between  nerve 
centers.     Thev  have  been  called  intracentral  nerves. 

436.  The  Nervous  Discharge.  —  When  a  nervous  impulse 
reaches  a  nerve  cell,  a  remarkable  change  takes  place. 
Something  similar  to  an  explosion  occurs,  and  a  new, 
different,  and  more  powerful  current  issues  from  the  cell. 
An  afferent  impulse  arrives  at  a  nerve  center;  that  change 
which  is  called  the  nervous  discJuvr/e  takes  place;  energy 
is  set  free  which  is  conducted  by  eft'erent  libers  to  the 
terminal  plate  in  a  muscle  fiber,  it  may  be.  Here  again 
a  second  nervous  discharge  results,  and  a  still  larger 
amount  of  force  is  liberated. 


300  THE    NERVOUS   SYSTEM 

437.  Functions  of  the  Spinal  Cord.  —  A  nerve  center  is  a 
group  of  nerve  cells  which  join  together  in  some  particular 
form  of  nervous  action.  The  gray  matter  of  the  spinal 
cord  is  a  series  of  nerve  centers,  while  the  white  matter 
is  arranged  in  bundles  of  nerve  fibers  whose  function  is, 
like  that  of  the  nerves  themselves,  the  transmission  of 
impulses. 

Two  sets  of  functions  belong  to  the  spinal  cord.  It  is 
the  channel  by  which  volitions  of  the  brain  are  conveyed 
to  many  of  the  muscles,  and  the  channel  by  which  many 
sensory  impulses  reach  the  brain ;  that  is,  by  means  of 
the  cord  voluntary  action  takes  place,  and  by  means  of  it 
sensory  impulses  are  transmitted. 

Another  set  of  functions  belonging  to  both  the  spinal 
cord  and  the  brain  is  the  production  of  reflex  action.  Some 
writers  upon  physiology  maintain  that  all  nervous  action 
is,  in  the  final  analysis,  reflex,  and  due,  more  or  less 
remotely,  to  external  stimulus,  what  is  called  mind  not 
being  able  to  originate  any  nervous  impulses  whatever. 
Others  support  the  opposite  view,  that  all  nervous  action 
is  voluntary  in  the  beginning,  and  becomes  reflex  by  prac- 
tice, either  on  the  part  of  the  individual,  or  on  that  of 
previous  generations  of  ancestors,  by  whom  the  tendency 
to  act  in  certain  ways  has  been  transmitted  to  their  de- 
scendants. This  is  not  the  place  for  a  discussion  of  such 
a  question,  and  we  may  accept  the  usual  distinction 
between  voluntary  and  reflex  action,  the  latter  being 
invariably  the  result  of  an  impression  received  from 
without. 

438.  Reflex  Action.  —  By  reference  to  Figs.  48  and  52, 
on  pp.  72  and  90,  the  course  of  a  nervous  impulse  in 
reflex  action  may  be  traced.  A  nerve  is  stimulated  at 
the   surface,    the   impulse    is    conveyed    by   the   afferent 


FUNCTIONS   OF  THE   NERVOUS   SYSTEM  301 

sensory  fibers  of  the  nerve  through  the  posterior  root  to 
the  spinal  cord.  There  it  may  pass  up  to  the  brain 
(Fig.  52)  in  one  of  the  white  columns  of  the  cord,  and, 
affecting  certain  cells  in  the  cortex,  result  in  conscious- 
ness and  sensation,  followed  by  voluntary  motion.  Or 
it  may  reach  directly  certain  cells  in  the  posterior  horn 
of  gray  matter  in  the  cord,  and  be  thence  transmitted  by 
communicating  fibers  across  to  other  cells  in  the  anterior 
horn,  from  which  a  motor  impulse  is  sent  forth  to  certain 
muscles,  and  they  are  called  into  action.  By  this  shorter 
path  motion  takes  place  without  necessarily  affecting  con- 
sciousness, and  without  the  interference  of  the  brain  ; 
that  is,  the  nerve  cells  in  the  cord  which  receive  the 
stimulus  reflect  the  impulse  to  other  cells  of  the  cord, 
which  then  issue  motor  orders,  without  waiting  for  in- 
structions from  the  overruling  brain.  It  is  as  if  the  cap- 
tain of  a  company  of  soldiers  in  a  great  army,  having 
received  from  incoming  scouts  news  of  an  attack  by  hostile 
forces,  immediately  orders  his  men,  without  waiting  for 
orders  from  his  superior  officers,  to  turn  upon  the  enemy 
and  repulse  them. 

The  medulla  oblongata  is  also  a  great  reflex  center, 
very  many  afferent-efferent  circuits  being  completed  there 
without  affecting  the  higher  cerebral  centers. 

439.  Examples  of  Reflex  Action.  —  If  a  sudden  flash  of 
light  strikes  the  eyes,  the  lids  are  immediately  closed. 
Any  part  of  the  body  touching  a  hot  object  is  at  once 
drawn  back.  A  person  in  sleep  may  raise  his  hand  to 
brush  away  a  fly  from  his  face,  or  he  may  start  at  a  sud- 
den noise  whether  awake  or  asleep.  All  these  acts  may 
take  place  without  conscious  orders  from  the  brain.  Many 
of  the  vital  processes  are  wholly  or  mainly  reflex  acts. 
Of  most  of  them  we  are,  in  health,  wholly  unconscious. 
macy's  phys.  — 19 


802  THE   NERVOUS   SYSTEM 

The  spinal  cord  centers,  or  those  of  the  medulla,  send 
efferent  impulses  to  the  glands  that  they  may  secrete  the 
digestive  juices,  when  afferent  impulses  have  been  excited 
by  food  taken  into  the  mouth  or  the  stomach.  The  mus- 
cular movements  of  the  alimentary  canal,  called  peristal- 
sis, are  reflex.  So  are  the  contraction  and  dilation  of 
the  blood  vessels  in  response  to  sensations  of  temperature 
conveyed  by  afferent  nerves  to  the  reflex  centers.  The 
growth  of  the  cells  throughout  the  body  is  also  presided 
over  by  these  centers. 

The  muscular  movement  of  reflex  action  is  often  greatly 
out  of  proportion  to  the  strength  of  the  stimulus  received. 
A  slight  irritation  of  the  mucous  membrane  of  the  trachea 
may  result  in  a  fit  of  coughing  so  violent  as  to  bring  into 
action  most  of  the  muscles  of  the  trunk  and  limbs.  The 
mere  prick  of  a  pin  may  cause  a  man  to  bound  from  his 
chair  and  execute  a  series  of  movements  involving  hun- 
dreds of  muscles.  It  is  as  if  the  nervous  irritation^ which 
is  brought  by  an  afferent  nerve  to  one  of  the  nerve  centers 
overflowed  the  cells  and  fibers  of  that  segment  and  stimu- 
lated neighboring  centers  also. 

440.  Voluntary  Movements  may  become  Reflex.  —  When  a 
child  begins  to  learn  to  walk,  each  separate  movement  is 
slowly  and  carefully  directed  by  the  intelligence  of  the 
brain.  In  time,  however,  the  brain  is  relieved  by  the 
spinal  cord  of  nearly  all  attention  to  the  locomotion  of 
the  body,  and  action  which  was  once  voluntary  is  better 
done  under  control  of  the  reflex  centers.  If  we  undertake 
to  descend  a  stairway  rapidly,  watching  and  directing  each 
step  by  the  will,  we  are  far  more  likely  to  make  a  misstep 
and  fall  than  if  we  pay  no  attention  to  the  separate  move- 
ments required.  So  in  performing  upon  musical  instru- 
ments, in  writing  with  a  pen  or  a  typewriter,  or  in  riding 


FUNCTIONS    OF   THE    NERVOUS   SYSTEM  303 

a  bicycle,  the  movements  at  first  slow  and  toilsome  become 
rapid  and  unconscious  as  well  as  more  accurate  by  prac- 
tice, which  places  them  under  the  direction  of  the  spinal 
cord  instead  of  the  brain.  They  become,  as  we  say, 
"automatic,"  instead  of  voluntary. 

441.  Advantages  of  Reflex  Action.  —  By  this  provision  for 
independent  action  in  the  spinal  nerve  centers  the  brain  is 
relieved  of  a  great  amount  of  labor,  and  so  given  leisure 
for  the  more  important  energies  of  life.  Then,  as  the 
spinal  cord  can  act  more  promptly  than  the  brain,  it  is 
better  able  to  protect  us  from  sudden  injury.  If  we  had 
to  wait  till  the  brain  ordered  the  muscles  of  the  arm  to 
pull  the  hand  out  of  the  fire,  we  might  often  be  seriously 
burned. 

A  thorough  education  of  the  spinal  cord  in  respect  to 
a  wide  variety  of  reflex  movements  greatly  extends  a 
man's  useful  and  enjoyable  activities. 

442.  Voluntary  Control  of  Reflex  Action.  —  Although 
what  are  called  reflex  actions  take  place  largely  without 
the  interference  of  the  will,  it  does  not  follow  that  any 
distinct  arbitrary  line  of  demarkation  can  be  drawn 
between  reflex  and  voluntary  acts.  In  playing  the 
piano,  for  instance,  the  rapid  and  complex  movements 
required  are  to  a  certain  extent  voluntary  as  well  as 
reflex,  though  the  cells  of  the  nerve  centers  discharge 
without  waiting  for  the  reception  of  orders  from  the 
brain.  In  respect  to  a  large  number  of  reflex  acts  the 
will  is  able  to  exercise  a  restraining  influence  if  not  entire 
inhibition,  and  such  overruling  power  constitutes  self- 
control.  A  child  may,  by  reflex  action,  utter  piercing 
screams  at  sight  of  what  he  judges  to  be  a  dangerous 
object,  and  may  even  be  thrown  into  convulsions  by  terror  ; 
but  when  he  has  become  a  man  —  if  he  has  received  proper 


304  THE   NERVOUS   SYSTEM 

training  —  he  will  have  acquired  voluntary  control  over 
his  muscles,  the  scream  will  be  restrained,  and  his  muscles 
will  remain  quiet,  or  will  remove  him  from  the  dangerous 
spot  according  to  the  direction  of  his  brain.  Many  a  sol- 
dier has  thrown  down  his  gun  and  beat  an  inglorious 
retreat  from  the  scene  of  his  first  battle,  and  yet  has  after- 
ward become  the  honored  veteran  of  many  a  hard-fought 
field.  A  child  may  roar  with  pain  and  clutch  with  all  his 
strength  at  the  dentist's  hand  when  his  first  tooth  is  drawn, 
while  men  have  been  known  to  endure  the  amputation  of 
a  limb  without  flinching.  Important  as  it  is  to  educate 
the  reflex  nervous  centers  to  the  supervision  of  swift  and 
accurate  useful  movements,  it  is  of  even  more  importance 
that  the  brain  should  still  be  able  to  exercise  a  superior 
restraining  power  wdien  needful  in  respect  to  even  those 
acts  which  may  be  ordinarily  left  to  the  reflex  centers. 

443.  Functions  of  the  Sympathetic  System.  —  Experiments 
have  shown  the  functions  of  the  sympathetic  system  to  be 
threefold. 

(1)  This  system  has  control  of  the  contractile  coats  of 
the  blood  vessels.  Certain  fibers,  called  "vasoconstrictors," 
carry  impulses  by  which  the  tone  of  the  walls  of  arteries 
and  veins  is  maintained.  If  the  sympathetic  nerve  is 
divided  in  the  neck,  there  is  a  general  dilation  of  the 
blood  vessels  on  the  same  side,  and  a  fall  of  blood  pres- 
sure in  the  arteries.  Other  fibers,  called  "  vasodilators," 
seem  to  possess  the  power  of  inJiihiting  the  action  of  the 
"constrictors,"  and  so  causing  dilation  of  the  vessels. 
A  large  part  of  the  action  of  the  vital  organs  is  controlled 
by  these  vasomotor  nerve  fibers  which  regulate  the  amount 
of  blood  distributed  to  those  organs. 

(2)  Other  fibers  of  the  sympathetic  nerves  seem  to  stimu- 
late directly  the  activity  of  secreting  cells  in  the  glands. 


FUNCTIONS   OF   THE   NERVOUS   SYSTEM  305 

(3)  Still  other  fibers  regulate  the  peristaltic  action  of 
stomach  and  intestines,  and  so  influence  digestion,  while 
others  influence,  to  some  extent,  the  process  of  respiration. 

The  sympathetic  nerves  affect  directly  only  involuntary 
processes. 

444.  Functions  of  the  Medulla  Oblongata.  —  The  whole  of 
the  brain  above  the  medulla  may  be  removed  from  an 
animal  without  killing  it.  Regular  and  rhythmical  respi- 
ration will  go  on,  the  heart  will  still  beat,  and  the  blood 
will  circulate,  wdiile  reflex  action  will  continue,  and  many 
muscles  will  contract  Avhen  the  sensory  nerves  connected 
Avith  them  are  irritated.  Still  more  complex  movements 
may  take  place.  If  food  is  placed  on  the  back  of  the 
tongue,  the  numerous  muscles  concerned  in  sv/allowing 
"will  be  excited  and  will  act  with  their  usual  accuracy. 
It  is  plain  that  all  these  reflex  movements  must  be  coor- 
dinated in  the  medulla  and  the  lower  centers.  An  animal 
living  thus,  by  the  action  of  the  nervous  centers  connected 
only  with  the  spinal  cord  and  the  medulla,  will  exist  by 
means  of  purely  reflex  mechanism  without  sensation  and 
without  intelligence. 

But  let  the  medulla  be  destroyed ;  respiration  will 
cease  (except  in  the  case  of  the  frog,  which  continues  to 
breathe  by  cutaneous  respiration),  and  death  will  almost 
instantly  follow.  The  nervous  center  to  wdiich  is  com- 
mitted the  coordination  of  respiratory  movement  has 
been  located  at  the  angle  of  the  wall  of  the  fourth  ven- 
tricle, and  that  point  has  been  called  the  vital  knot.  The 
medulla  may  be  divided  above  the  respiratory  center,  and 
the  action  of  the  muscles  of  the  chest  and  diaphragm  will 
be  unaffected.  Though  the  heart,  as  has  been  stated, 
will  continue  its  rhythmic  beat  for  a  time  after  all  con- 
nection with  cerebro-spinal  centers  has  been  severed,  still 


306  THE   NERVOUS    SYSTEM 

its  movements  are  much  modified  through  its  nervous 
communication  with  the  medulla.  Inhibitory  fibers  pass 
from  there  in  the  vagus  nerve,  and  if  that  is  cut  the 
heart's  motion  is  accelerated.  Accelerator  fibers  from 
the  medulla  pass  to  the  heart  through  the  spinal  cord  and 
the  sympathetic  nerves.  Their  destruction  or  severance 
from  the  center  in  the  medulla  slows  the  heart's  beat.  The 
medulla  oblongata^  then,  is  a  coordinating  center  for  those 
reflex  actions  upon  which  the  maintenayice  of  life  depends. 

445.  Besides  its  great  function  as  a  center  for  the 
reflex  action  connected  with  the  vital  processes,  the 
medulla  oblongata  also  acts,  like  the  cord,  as  a  conductor 
of  sensory  and  motor  impressions.  Motor  fibers  from  the 
upper  parts  of  the  brain  cross  in  the  anterior  pyramids 
of  the  medulla  and  descend  the  cord,  to  pass  out  in  the 
anterior  roots  of  spinal  nerves.  If  they  are  destroyed  on 
the  right  side  above  the  crossing,  paralysis  of  motion  of 
the  left  side  results  ;  while  section  of  the  fibers  -  on  the 
right  side  below  the  crossing  will  cause  paralysis  on  the 
right  side. 

446.  Functions  of  the  Pons  Varolii.  —  The  pons,  besides 
serving  as  a  passageway  for  afferent  and  efferent  impulses 
between  the  medulla  and  other  parts  of  the  brain,  contains 
imbedded  in  the  bundles  of  white  fibers  a  number  of 
nuclei  of  gray  matter  connected  with  the  roots  of  cranial 
nerves,  some  of  the  same  nerves  being  also  connected 
with  nuclei  in  the  medulla.  The  pons  is  to  be  regarded 
as  both  a  conductor  and  a  reflex  center,  and  also  as  a 
relay  center  between  the  cerebellum  and  the  cerebrum. 

447.  Functions  of  the  Cerebellum.  —  The  cerebellum  re- 
ceives impressions  through  its  three  pairs  of  peduncles 
by  which  its  hemispheres  are  connected  with  other  parts 
of  the  brain,  and  so  with  the  spinal  cord,  and  with  each 


FUNCTIONS   OF   THE   NERVOUS   SYSTEM  307 

other.  It  has  long  been  regarded  as  established  that  its 
special  function  is  to  act  as  a  center  —  not  the  sole,  but  the 
great  center  — for  coordination  of  muscular  movement^  and 
especially  for  that  coordination  of  muscles  necessary  to 
maintain  the  body  in  a  position  of  equilibrium.  This 
harmonious  adjustment  of  the  working  of  so  large  a 
number  of  muscles  requires  the  action  of  a  large  and 
complicated  nervous  mechanism,  involving  the  eyes,  por- 
tions of  the  auditory  apparatus,  and  the  apparatus  for 
touch,  as  well  as  the  muscular  sense  which  tells  us  what 
we  are  doing  with  our  muscles.  Sensory  impulses  from 
these  four  sources  reach  the  cerebellum  by  its  peduncles 
and  keep  it  informed  as  to  the  position  of  the  body  in 
space.  Then,  in  order  that  all  the  numerous  muscles 
involved  may  act  with  regulated  strength  and  in  mutual 
harmony  to  preserve  the  equilibrium,  the  nerve  centers 
m  each  half  of  the  cerebellum  send  on  afferent  impulses 
to  the  cerebral  hemisphere  of  the  opposite  side.  There 
takes  place  the  motor  discharge  which  sends  forth  the 
efferent  impulse  to  the  muscles.  In  the  process  of  select- 
ing the  muscles  which  are  to  act,  and  arranging  the  order 
and  amount  of  their  action,  the  gray  matter  of  the  higher 
centers,  of  the  basal  ganglia,  the  cerebellum,  and  the 
whole  of  the  spinal  cord  is  concerned. 

The  cerebellum  is  also  especially  involved  in  the  pro- 
duction of  the  finer  and  more  delicate  movements  of  the 
hand. 

448.  Functions  of  the  Corpora  Quadrigemina  and  the  Crura 
Cerebri. —  Of  the  functions  of  the  crura  cerebri^  or  pedun- 
cles of  the  cerebrum,  we  know  little  except  that  they  con- 
duct nervous  impulses.  If  one  peduncle  is  destroyed,  the 
animal  moves  toward  the  opposite  side,  round  and  round 
in  circles.     The  corpora  quadrigemina^  or  optic  lobes,  are  the 


308  THE   NERVOUS   SYSTEM 

first  portions  of  the  brain  to  receive  visual  impressions 
through  the  optic  tracts;  but  just  what  share  they  have  in 
vision  is  still  not  fully  determined.  We  know  that  they  are 
concerned  in  the  movements  of  the  iris  and  of  the  ciliary 
muscle,  and  there  are  indications  that  they  have  much 
to  do  with  the  consciousness  of  light  and  color.  It  may 
be  that  these  and  other  neighboring  ganglia,  having  re- 
ceived direct  impressions  from  the  retina,  originate  reflex 
movements  without  waiting  for  voluntary,  conscious  action 
of  the  higher  centers.  This  would  explain  the  uncon- 
scious sight  and  movements  of  the  somnambulist,  who 
sees,  without  knowing  it,  how  to  direct  his  steps  along 
dangerous  and  intricate  paths.  Destruction  of  the  cor- 
pora quadrigemina  causes  immediate  blindness. 

449.  Functions  of  the  Optic  Thalami.  —  The  ganglia  of  the 
optic  thalami  also  have  something  to  do  with  sight,  as 
serious  injury  to  them  invariably  results  in  disturbance 
or  destruction  of  vision.  There  is  also  evidence  that 
they  play  a  subordinate  part  in  connection  with  sensa- 
tion, and,  with  the  corpora  striata  and  conducting  fibers, 
establish  a  shorter  afferent-efferent  circle  which  does  not 
involve  the  higher  centers  of  the  brain,  but  whose  action 
results  in  consciousness  and  volition. 

450.  Functions  of  the  Cerebrum.  —  If  a  frog  be  entirely 
deprived  of  the  cerebral  hemispheres  and  left  quite  undis- 
turbed, it  will  sit  quietly  in  the  same  spot  forever.  Though 
it  breathes,  it  will  be  an  insensible,  immovable  lump  of 
matter.  It  may  be  surrounded  by  food,  but  it  w^ill  die 
of  starvation.  No  spontaneous  movement  is  possible  to 
it.  But  let  the  frog  be  touched,  and  it  will  move.  If 
gently  stroked,  it  will  croak.  If  its  foot  be  pinched,  it  will 
hop.  If  thrown  into  water,  it  will  swim  to  land.  A  sud- 
den movement  close  to  its  eyes  will  cause  it  to  draw  back. 


FUNCTIONS   OF  THE   NERVOUS   SYSTEM  309 

A  fish  under  similar  conditions  will  continue  to  swim 
in  a  straight  line  unless  obstacles  appear,  and  those  it 
will  avoid  as  usual.  Its  movement  will  be  kept  up  until 
ended  by  exhaustion.  It  will  never  pause  to  eat,  though 
abundance  is  on  every  side.  Like  the  frog,  the  fish  de- 
prived of  its  cerebrum  is  incapable  of  any  action  not  the 
result  of  immediate  and  direct  external  stimulus.  It 
swims  because  the  contact  of  the  water  with  the  surface 
furnishes  constant  irritation  to  the  swimming  mechanism. 
Corresponding  results  follow  experiments  upon  higher 
animals  and  observations  upon  man  himself.  The  lower 
nerve  centers  act  at  once  in  response  to  present  stimulus, 
and  act  without  necessarily  affecting  consciousness,  with- 
out sensation,  and  without  will. 

451.  The  frog  or  the  fish  retaining  the  whole  of  the 
brain  intact  responds  to  external  irritation,  but  the  pre- 
cise results  of  such  irritation  cannot  be  accurately  pre- 
dicted, and  the  action  may  be  deferred  for  a  longer  time 
than  when  the  cerebrum  is  wanting. 

In  the  higher  animals  the  varieties  of  possible  results 
of  stimulation  are  still  more  numerous.  Strike  a  wild 
cat  over  the  nose  with  a  club  and  he  may  turn  and  flee, 
or  he  may  plunge  forward  and  bury  his  teeth  in  your 
body.  The  nervous  discharge  in  all  these  cases  will, 
however,  be  likely  to  take  place  with  considerable  prompt- 
ness in  one  way  or  another. 

But  suppose  a  man  to  receive  a  severe  injury  or  insult. 
He  may  retaliate  at  once  by  shooting  or  knocking  down 
his  assailant,  or  he  may  cherish  a  sense  of  wrong  for  many 
years,  seeking  opportunity  for  revenge.  He  may  even 
inculcate  the  enmity  upon  the  minds  of  his  children,  to  be 
passed  on  from  generation  to  generation  as  a  family  feud. 
In  man,  therefore,  and  to  some  extent  in  the  higher  ani- 


810  THE   NERVOUS   SYSTEM 

mals  also,  we  find  the  singular  power  of  postponing,  often 
for  an  indefinite  time,  the  reaction  which  in  the  lower 
animals  immediately  follows  stimulation.  Because  it  is 
impossible  to  trace'  all  nervous  reaction  to  an  incoming 
impulse,  we  must  not  thence  conclude  that  none  has  been 
received.  To  the  higher  cerebral  centers  alone,  that  is,  to 
the  gray  matter  of  the  cortex,  belongs  this  power  of  de- 
ferred action.  They  are  able  to  postpone  the  nervous 
discharge  which  results  from  incoming  impressions  until 
those  impressions  have  been,  as  we  may  say,  considered. 
The  nature  and  meaning  of  the  efferent  impulse  to  be 
issued  in  consequence  of  the  impulse  received  may  then 
be  decided  upon  after  long  deliberation  and  in  view  of 
very  remote  sensations. 

452.  The  cerebrum^  then,  is  the  seat  of  those  psychic  or 
mental  processes  which  are  called  consciousness^  perception^ 
volition^  memory^  thought^  imagination^  and  emotion.  These 
are  all  terms  which  in  the  present  state  of  knoAvledge 
belong  rather  to  psychology  than  to  physiology.  They 
have  an  undeniable  physical  basis,  but  to  what  extent  they 
depend  upon  material  facts  and  physical  laws,  we  do  not 
know.  Consciousness  may  be  said  to  be  the  knowledge 
which  the  mind  has  of  its  own  operations  and  conditions. 
Physiologically  speaking,  it  has  been  called  "  the  final 
phase  of  sensory  impressions."  Perception  is  the  recogni- 
tion by  the  mind  of  impressions  received  through  sensory 
nervous  tracts.  Volition.,  so  far  as  it  is  physiological,  is 
the  impulse  in  the  cerebral  hemispheres  which  originates 
motor  activity.  Memory  may  be  called  the  power  of  stor- 
ing up  nervous  impressions  and  making  them  at  some 
indefinite  later  period  the  cause  of  efferent  influences. 
Perhaps  we  need  not  go  further  in  the  attempt  to  give 
physiological  definitions  to  metaphysical  terms. 


FUNCTIONS   OF   THE   NERVOUS   SYSTEM  311 

453.  Localization  of  Functions  in  the  Cortex.  —  The  area 
of  the  cortex,  with  all  its  convolutions,  is  in  man  about 
four  square  feet.  In  the  lowest  vertebrate  animals  the 
surface  of  the  brain  is  smooth,  but  as  animals  rise  in  the 
scale  of  intelligence  fissures  and  folds  appear,  growing 
more  complex  and  more  like  those  of  man,  till  in  the  brain 
of  the  highest  apes  a  striking  resemblance  is  seen  to  that 
of  man. 

The  w^hole  surface  of  the  human  cortex  has  now  been 
mapped  out  into  tracts,  or  districts,  to  many  of  which  it  is 
found  that  special  functions  are  assigned.  Post-mortem 
examination  of  diseased  human  brains,  together  with  close 
study  of  the  effects  of  disease  during  life,  and  numer- 
ous experiments  by  vivisection  upon  animals,  —  especially 
upon  the  monkey  as  possessed  of  a  brain  of  the  same 
type  as  that  of  man, — have  resulted  in  greatly  extend- 
ing our  knowledge  respecting  this  localization  of  func- 
tions in  the  cortex.  We  cannot  follow  the  method  and 
progress  of  discovery,  but  some  of  the  conclusions  have 
been  referred  to  in  preceding  chapters  and  others  may 
be  mentioned  here. 

In  respect  to  some  of  the  highest  mental  operations 
the  brain  probably  acts  as  a  whole  through  the  immense 
number  of  associational  fibers  connecting  all  parts  of  the 
cortex,  so  that  no  physiologist  is  able  to  say  that  thought 
is  located  in  certain  cells  of  that  convolution,  or  memory 
or  imagination  in  another.  But  it  is  still  correct  to  say 
that  certain  groups  of  cortical  cells  are  concerned  in  a 
peculiar  way  with  certain  sensations  or  with  certain 
movements. 

454.  Motor  Areas.  —  It  has  been  found  that  when  the 
surface  of  an  animal's  brain  is  laid  bare  and  an  electric 
current  is  applied  to  the  convolutions,  the  stimulation  of 


312 


THE   NERVOUS   SYSTEM 


the  same  spot  in  the  cortex  is  always  followed  by  the 
same  movement  in  the  same  animal.  Those  portions  of 
the  cortex,  therefore,  whose  stimulation  results  in  motion, 
are  called  motor  areas.  Sjjeaking  generally,  these  motor 
areas  may  be  said  to  occupy  the  portion  of  the  cortex 
about  the  fissure  of  Rolando  and  along  the  middle  surface, 
or  edge,  of  the  hemispheres.  Particular  movements  of 
head,  trunk,  and  limbs  are  associated  with  particular  spots 
in  the  surface  of  this  region,  as  shown  in  Fig.  138.  The 
area  controlling  articulate  speech,  that  is,  the  movements 


Fig.  138. —Diagrams  illustrating  localization  of  function  in 
the  cerebrum. 


I  outer  surface  of  left  hemisphere. 
II  inner  surface  of  right  hemisphere. 

Motor  areas  are  shaded. 
Cc  corpus  callosum. 
Fr  frontal  lobe. 


Oc  occipital  lobe. 
Pa  parietal  lobe. 
Ro  fissure  of  Rolando. 
Sy  Sylvian  fissure. 
Te  temporal  lobe. 


of  tongue,  lips,  etc.,  in  speech,  lies  adjacent  to  the  Sylvian 
fissure  on  the  lowest  frontal  convolution.  And,  what  is 
X^eculiar  to  this  cortical  area  for  speech,  it  appears  to  be 
confined  to  a  single  hemisphere  —  in  most  cases  the  left 
—  instead  of  being  bilateral  as  are  other  parts  of  the 
brain. 

455.  Sensory  Areas  in  the  cortex  are  less  definitely 
located  than  are  the  motor  areas.  Broadly  speaking,  they 
lie  behind  the  motor  surfaces. 


FUNCTIONS   OF  THE   NERVOUS  SYSTEM  313 

The  area  for  vision  is  in  the  occipital  lobe.  If  this  area 
be  diseased,  blindness  of  half  of  each  retina  on  the  same 
side  results. 

The  auditor?/  area  is  believed  to  lie  in  the  upper 
portion  of  the  temporal  lobe  ;  the  areas  for  taste  and 
smell  on  the  under  and  inner  side  of  the  same  lobe. 
Tactile  sensations  have  been  located  in  certain  portions  of 
the  under  surface  of  the  occipital  lobe  ;  but  most  recent 
experiments  indicate  that  some,  at  least,  of  the  sensory 
fibers  end  in  what  has  been  called  the  motor  area  about 
the  fissure  of  Rolando.  If  that  is  established,  it  Avill 
appear  that  the  fibers  connected  with  conscious  sensation 
are  in  close  association  Avith  those  which  convey  voluntary 
motor  impulses,  and  the  Rolandic  area  will  be  more 
properly  termed  the  sensori-motor  area. 

456.  It  will  be  noticed  that  in  the  map  of  the  cortex  a 
large  portion  of  the  front  of  the  brain  remains,  like  great 
tracts  of  land  in  Central  Africa  upon  old  geographical 
maps,  without  names  and  internal  divisions.  They  are 
unexplored  or,  at  least,  unknown  regions.  No  specific 
functions  can  be  positively  assigned  to  those  frontal  con- 
volutions of  the  cerebrum.  An  animal  deprived  of  them 
appears  to  suffer  little  inconvenience  in  consequence,  and 
in  one  well-known  case  where  a  man  lost  the  frontal  por- 
tion of  his  brain  in  an  explosion  of  dynamite,  full  recovery 
followed  without  any  permanent  noteworthy  consequences. 
It  is  a  favorite  theory  with  some  that  the  frontal  convolu- 
tions are  the  seat  of  the  intellectual  faculties,  but  the 
theory  has  not  been  confirmed. 


CHAPTER   XXIII 
HYGIENE  OF  THE    NERVOUS    SYSTEM 

457.  It  is  often  remarked  in  recent  years,  though  per- 
haps without  sufficient  evidence,  that  nervous  diseases  are 
rapidly  increasing.  Cases  of  insanity,  nervous  prostra- 
tion, insomnia,  of  mental  and  nervous  weakness  of  various 
kinds,  are  at  any  rate  so  numerous  as  to  give  occasion  for 
anxious  inquiry  as  to  the  probable  future  of  our  race.  It 
is,  then,  of  the  utmost  importance  that  we  should  know 
how  to  order  our  lives  so  that  our  nervous  systems  may 
be  preserved  in  health  and  vigor.  All  the  bodily  actions 
are  dependent  upon  the  reception  of  nervous  stimulus  at 
the  right  time,  the  right  place,  and  in  due  amount,  and 
when  that  fails,  or  is  in  any  way  deranged,  the  whole  sys- 
tem suffers. 

458.  Nervousness  fs  not  to  be  understood  as  a  sign  of  a 
particularly  refined  and  delicate  nervous  constitution.  It 
is  due  to  a  lack  of  control  by  the  higher  nerve  centers  and 
is  always  an  indication  of  weakness  or  disease;  always  to 
be  fought  against  by  all  reasonable  means,  and  never  to  be 
accepted  as  a  necessary  feature  of  a  sensitive  organization. 

459.  Nutrition  of  the  Nervous  System.  —  Skillful  and  experi- 
enced physicians  tell  us  that  true  nervous  diseases,  that 
is,  disorders  attended  by  actual  degeneration  or  structural 
changes  in  nervous  matter,  are  comparatively  rare,  and 
when  they  do  occur  are  due  to  lack  of  nutrition  rather 

314 


HYGIENE   OF  THE  NERVOUS    SYSTEM  315 

than  to  excessive  demands  upon  the  nervous  organism. 
No  part  of  the  system  is  so  carefully  protected  from 
injury,  so  hedged  about  and  guarded  from  evil  influences 
of  every  sort,  as  are  the  precious  nerve  centers.  The  nerv- 
ous mechanism  is  the  last  to  waste  when  the  body  dies 
from  starvation,  and  under  such  conditions  it  is  probably 
supported  at  the  expense  of  other  tissues  as  being  more 
important  than  they. 

Recalling  what  we  have  learned  from  previous  study  we 
shall  see  clearly  the  importance  and  the  source  of  nour- 
ishment for  the  nerve  cells.  It  is  by  the  blood  alone  that 
they  are  fed.  Every  thrill  of  nervous  influence  destroys 
tissue,  and  unless  an  abundance  of  pure  arterial  blood  is 
at  hand  for  rebuilding  the  cells,  weakness  and  decay  will 
follow.  Diseases  which  lead  to  blood  poisoning  —  as 
pneumonia  and  typhoid  fever  —  are  accompanied  wdth 
delirium,  weakening  of  the  mental  faculties,  or  other  nerv- 
ous symptoms. 

460.  In  order  that  pure  blood  may  be  furnished,  the 
regular  and  perfect  action  of  the  digestive  organs  is  in- 
dispensable. Digestion  is  a  slow  process ;  it  cannot  be 
hastened.  If  we  eat  our  food  so  rapidly  that  it  is  not 
subjected  to  the  action  of  the  saliva,  and  is  not  properly 
divided  by  the  teeth,  the  gastric  juice  will  not  be  able  to 
effect  the  necessary  changes  in  the  stomach,  especially  if 
we  hasten  to  call  the  blood  away  for  other  work  too  soon, 
and  the  food  will  pass  on  into  the  intestines  only  half 
ready  for  the  work  of  the  other  juices.  Even  in  a  healthy 
man  the  normal  processes  in  the  alimentary  canal  develop 
an  amount  of  poison  sufficient  to  kill  him  if  it  is  not  neu- 
tralized by  the  products  of  the  liver,  pancreas,  and  other 
organs,  which  nature  provides  for  that  purpose.  So,  if 
those  secretions  are  interfered  with,  —  as  they  are  by  the 


316  THE   NERVOUS   SYSTEM 

use  of  alcohol,  for  instance,  —  or  fail  of  their  due  action 
upon  the  food  because  the  preceding  processes  are  incom- 
plete, the  nutriment  poured  into  the  blood  stream  may 
carry  disease  instead  of  health  and  vigor  to  brain  and 
nerve.  It  is  just  such  inconsiderate  habits  in  respect  to 
eating  which,  as  physicians  well  know,  have  led  to  many 
a  serious  case  of  "  nervous  prostration  "  among  business 
men  or  students. 

461.  But  the  blood  cannot  be  kept  pure  without  a  con- 
stant supply  of  pure  air  in  the  lungs.  If  that  is  lacking, 
there  is  at  once  defective  nutrition  of  the  nerve  cells. 
Undoubtedly  the  nervousness  so  common  among  women 
is  due,  more  than  to  any  other  one  cause,  to  an  insufficient 
supply  of  pure  air  for  the  lungs.  Tight  clothing  which 
restricts  the  capacity  of  the  chest,  lack  of  outdoor  exer- 
cise, and  the  breathing  of  vitiated  and  usually  (in  winter) 
too  warm  air  are  all  direct  causes  of  nerve  weakness. 

462.  One  more  condition  is  necessary  in  order  tl^t  the 
blood  may  be  pure,  and  that  is  a  healthy  activity  of  the  ex- 
cretory mechanisms.  If  the  worn-out  material  from  the 
wasting  tissues  is  not  removed,  it  will  remain  to  clog  and 
poison  the  vital  current.  In  a  word,  the  condition  of  the 
brain  and  spinal  cord,  and  the  vigor  and  readiness  of  nerv- 
ous reaction,  depend  wholly  upon  the  distribution  and 
quality  of  the  blood,  and  those  depend  upon  food,  diges- 
tion, respiration,  and  excretion.  It  is  true  that  a  man 
does  not  die  at  once  or  become  diseased  because  he  has 
eaten  improper  food  or  breathed  foul  air.  The  physical 
organism  has  marvelous  powers  for  contending  against 
unfavorable  conditions,  a  wonderful  way  of  throwing  off 
poison  and  rebounding  from  depression,  so  long  as  the 
natural  vigor  of  tissues  is  not  impaired  by  persistent 
abuse.     But  for  each  individual  there  is  a  point  beyond 


HYGIENE   OF  THE   NERVOUS   SYSTEM  317 

which  recuperation  becomes  doubtful,  wholly  impossible, 
or  only  partial. 

463.  Fatigue  of  Nerve  Cells.  —  A  certain  amount  of  activ- 
ity in  cells  of  all  sorts  is  promotive  of  health.  It  causes 
a  more  rapid  flow  of  the  blood  and  greater  storage  of 
fresh  matter  to  be  afterward  used  in  the  liberation  of 
energy.  But  too  prolonged  exercise  or  stimulation  leads 
to  exhaustion  of  the  cells,  and  for  every  one  there  is  a  limit 
to  the  power  of  restoration  after  exercise.  In  the  last 
stages  of  extreme  fatigue  it  is  the  nerve  cells  and  not  the 
muscles  which  succumb  to  exhaustion.  Microscopic  exam- 
ination of  animals  shows  that  the  cells  of  the  nerve  centers 
gradually  become  shrunken  and  irregular  in  outline  under 
stimulation,  while  the  nuclei  within  the  cells  and  in  the 
inclosing  wall  are  also  seen  to  diminish.  After  refreshing 
sleep  the  cells  are  at  their  full  size,  the  blood  current  passes 
at  the  normal  rate  through  the  nerve  centers,  and  they 
readil}'  respond  to  stimulus.  At  the  close  of  the  day  a 
marked  chano-e  has  occurred  in  the  cells  of  those  centers. 
The  rate  of  blood  circulation  has  declined,  and  the  stream 
is  loaded  with  the  accumulated  products  of  the  day's  activ- 
ities, while  the  diminished  size  of  the  nerve  cells  and  their 
nuclei  proclaims  a  state  of  fatigue. 

464.  Sleep.  —  It  is  by  means  of  sleep  that  the  nerve  cells 
regain  their  form  and  their  readiness  to  react  on  receiving 
stimulus.  During  sleep  the  nervous  activities  are  greatly 
diminished.  Afferent  impulses  do  not  set  in  motion  the 
complex  cerebral  processes  of  waking  hours.  Conscious- 
ness is  not  excited,  and  memory  fails  to  register  the  recep- 
tion of  impulses.  Reflex  movements  may  indeed  result, 
but  in  the  deepest  sleep  even  such  action  is  mainly  lack- 
ing. Respiration  and  the  circulation  of  the  blood  con- 
tinue, but  become  slower,  and  a  large  amount  of  blood  is 

macy's  phys.  — 20 


318  THE   NERVOUS   SYSTEM 

withdrawn  from  the  brain.  Much  of  the  internal  muscu- 
lar and  secretory  mechanism  becomes  comparatively  inac- 
tive. The  whole  body  is  affected  by  the  changes  brought 
about  by  sleep.  We  may  describe  the  effects  of  sleep, 
though  we  are  not  able  to  tell  what  sleep  is,  or  what  are 
its  causes. 

That  sleep  is  essential  to  the  life  of  all  those  animals 
having  a  well-developed  nervous  system  we  know.  Con- 
tinued loss  of  sleep  in  man  results  in  insanity  and  death 
much  sooner  than  death  follows  starvation.  Regular 
periods  of  sleep  are  needful,  and  nature  provides  for  rest 
to  the  brain  by  gradually  reducing  the  amount  of  blood 
circulating  there  when  the  accustomed  hour  for  repose 
draws  near.     Then,  as  we  say,  we  become  "sleepy." 

465.  Necessary  Amount  of  Sleep. —  Sleep,  to  be  recupera- 
tive, should  continue  uninterrupted  for  several  hours.  It 
has  been  shown  by  experiments  upon  certain  animals  that 
usually  four  hours  or  more  are  needed  to  reconstruct  the 
shrunken  cells.  Short  "  naps,"  even  though  the  aggregate 
be  sufficient,  do  not  restore  and  refresh  the  system  as  does 
continuous  sleep.  If  the  nerve  cells  are  forced  to  work 
again  before  being  fully  restored,  they  do  so  under  great 
disadvantages.  Growing  children  require  more  sleep 
than  adults,  and  a  healthy,  active  child  is  not  likely  to 
take  more  than  is  good  for  him.  For  adults  who  work 
vigorously  with  muscles  or  brain,  the  old  rule  of  eight 
hours  is  a  safe  one,  though  many  are  satisfied  with  less. 
Much  depends  upon  habit  and  individual  peculiarities. 
The  old  usually  need  less  sleep  than  others.  The  proc- 
esses of  growth  are  long  since  completed,  the  activities 
of  life  are  less,  vital  processes  go  on  more  slowly,  and 
complete  repair  of  the  various  tissues  no  longer  takes 
place. 


HYGIENE   OF   THE   NERVOUS   SYSTEM  319 

466  How  to  induce  Sleep.  —  Insoniiiia  has  become  so  com- 
mon of  late  that  special  attention  should  be  paid  to  ways 
of  promoting  sleep.  A  great  variety  of  drugs  are  used 
for  the  pur2)ose,  but  some  of  them  are  extremely  danger- 
ous, and  none  of  them  should  ever  be  taken  except  by  the 
advice  of  a  competent  physician.  Any  activity  of  cells,  any 
production  of  energy,  —  nervous  energy  as  well  as  other 
forms,  —  gives  rise  to  certain  substances  harmful  to  the 
body.  By  natural  provision  the  presence  of  this  waste 
matter  in  the  blood  causes  a  feeling  of  fatigue  which  in- 
clines to  a  lessening  of  activity  and  gives  opportunity  for 
recuperation.  To  promote  sleep,  we  cut  off  so  far  as  possi- 
ble the  various  sources  of  stimulus  to  the  nerves.  We 
recline  at  full  length  that  the  trunk  muscles  may  be  relieved 
from  the  effort  to  preserve  the  equilibrium.  We  remove  all 
burdensome  or  uncomfortable  clothing  Avhich  might  con- 
stantly excite  the  nerves  of  the  skin.  A  warm  bath  just 
before  retiring  tends  to  allay  external  irritation  and  helps 
to  withdraw  the  blood  from  the  head.  We  darken  the 
room  and  close  the  door  against  noise.  For  some  hours 
before  retiring  our  occupations  should  be  free  from  excite- 
ment. One  who  is  inclined  to  sleeplessness  should  do  no 
evening  br^in  work.  A  serene  frame  of  mind  conduces 
to  repose.  Although  late  and  heavy  meals  are  not  to  be 
recommended,  it  has  been  found  that  to  eat  moderately  of 
easily  digested  food  at  bedtime  will  sometimes  withdraw 
the  blood  from  the  brain  and  dispose  to  sound  sleep. 
Active  physical  exercise  during  the  day,  sufficient  to  cause 
fatigue  of  the  muscles,  is  usually  followed  by  restful  sleep. 
For  brain  workers  a  short  period  of  active  exercise  before 
retiring  —  a  quick  walk  or  practice  with  dumb-bells  or 
Indian  clubs  —  may  promote  sleep.  So  may  a  hot  foot- 
bath, or  vigorous  rubbing  of  the  feet  and  legs,  or  other 


320  THE   NERVOUS   SYSTEM 

massage.  Other  means  for  accomplishing  the  object  of 
diverting  the  blood  from  the  brain  will  occur  to  one  who 
gives  the  subject  thought. 

A  keeping  room  should  be  well  ventilated,  dark,  and 
quiet,  the  bed  not  too  soft,  nor  the  covering  too  abundant. 
A  habit  of  going  to  sleep  may  be  cultivated  by  lying 
down  only  at  times  when  one  wishes  to  sleep.  By  the 
laws  of  association  the  reclining  posture  will  come  to  aid 
in  inducing  the  cerebral  condition  desired. 

467  "  Overwork."  —  It  is  common  to  attribute  most  of 
the  nervous  disorders  of  our  time  to  the  overtaxing  of  the 
brain  and  nerves  in  business  or  study,  or  to  excessive 
strain  of  the  nervous  system  from  anxiety  or  care.  No 
doubt  such  cases  occur,  but  other  causes  are  far  more 
prolific  than  these.  The  nervous  system  seems  to  be 
constructed  to  last  as  long  as  it  receives  nourishment 
enough  and  is  allowed  sleep  enough.  Among  students 
there  occur  frequent  cases  of  nervous  derangement  which 
could  be  traced,  if  all  the  facts  were  known,  to  causes 
other  than  overstudy.  To  keep  a  brain  in  health  it  must 
be  used.  Even  severe  mental  application  is  promotive  of 
health  if  practiced  under  healthful  conditions.  A  student 
may  break  down  because  he  uses  his  brain  without  taking 
sufficient  sleep,  exercise,  and  food  to  keep  it  in  good  con- 
dition, or  fails  properly  to  vary  the  kind  of  mental  effort ; 
but  if  he  follows  the  various  suggestions  upon  these  points 
given  in  this  book,  he  can  hardly  do  so.  There  is  no 
patent  "brain  food"  which  will  supply  the  nerve  cells 
with  nutriment  for  their  activities  if  it  does  not  also  build 
up  all  the  other  organs.  The  human  life  is  one  life.  If 
one  member  suffers,  all  the  members  suffer.  One  cannot 
cultivate  the  brain  into  vigorous  health  while  neglecting 
or  abusing  the  stomach,  the  lungs,  and  other  organs. 


HYGIENE   OF  THE   NERVOUS   SYSTEM  321 

Proper  habits  of  study  should  be  acquired.  One  should 
learn  to  bring  all  his  mental  force  to  bear  upon  the  work 
in  hand — to  concentrate  his  thoughts,  as  we  say;  that  is, 
to  hold  his  attention  firmly  upon  the  subject  before  him, 
and  not  dawdle  over  his  book,  letting  his  thoughts  run 
from  one  topic  to  another  according  to  chance  sugges- 
tions, coming  back  only  now  and  then  to  his  work.  Such 
practices  weaken  the  brain  and  unfit  it  for  effective  labor. 
Severe,  intense  mental  effort  for  a  short  time  should  be 
the  rule,  and  then  relaxation  or  complete  change  in  the 
form  of  labor.  But  bad  mental  habits,  abuse  of  the 
digestive  organs,  and  the  breathing  of  impure  air  are  not 
the  only  causes  of  injury  to  brain  and  nerves.  A  life 
of  overexcitement,  which  keeps  the  nerves  continually 
a  quiver  in  response  to  incessant  stimulation,  has  shattered 
the  nervous  system  of  many  a  girl  or  young  woman.  Our 
American  customs  leave  to  the  young  too  little  space 
for  the  quiet,  regular,  uneventful  living  which  promotes 
health  of  mind  and  body,  strengthens  for  future  useful- 
ness, and  stores  energy  for  the  severe  and  sudden  emer- 
gencies of  mature  life.  If  a  girl  breaks  down  in  health 
during  her  school  years,  her  teachers  are  usually  blamed 
as  exacting  too  much  brainwork,  whereas  the  mischief  is, 
in  fact,  far  oftener  due  to  unhygienic  habits  of  life,  to  too 
rich  or  otherwise  unsuitable  food,  to  lack  of  air  and  exer- 
cise, and,  especially,  to  too  much  social  indulgence,  along 
with  late  hours  which  interfere  with  regular  and  abundant 
sleep  and  use  up  the  nervous  force  which  should  be  given 
to  study  or  stored  for  the  future. 

468.  Habit  as  connected  with  Nervous  Action.  —  Something 
was  said  upon  this  subject  when  reflex  nervous  action  was 
considered,  but  its  importance  is  so  great  that  it  should 
be  further  dwelt  upon. 


322  THE   NERVOUS   SYSTEM 

Habit  is  a  law  or  property  of  the  material  world,  and 
all  our  habits  of  life  and  action,  mental  as  well  as  phj^sical, 
are  now  understood  to  have  their  basis  in  the  ph3^sical 
constitution  of  our  bodies.  The  particles  of  matter  which 
compose  inorganic  bodies  act  and  react  upon  one  another 
in  a  certain  way,  and  ever  after  they  act  and  react  in  that 
same  way  more  easily,  that  is,  with  less  resistance  than  in 
other  ways,  and  by  repetition  of  this  action  a  habit  is 
established.  In  organic  bodies  this  property  is  still  more 
marked.  A  pathway  of  discharge  of  nervous  influence 
in  the  brain,  once  formed,  is  afterward  the  channel  by 
which  efferent  nervous  currents  tend  to  pass  outward. 
All  our  activities  are  due  to  this  streaming  outward  of 
nervous  currents  excited  by  the  constant  streaming  inward 
of  other  nervous  currents,  or  by  stimulation  originating 
in  the  brain  itself.  A  new  channel  once  made  for  the  out- 
ward flow  becomes  the  path  of  least  resistance  for  the 
next  wave,  which  deepens  the  bed  of  the  stream  and  de- 
termines more  surely  the  course  of  following  impulses. 
In  course  of  time  the  nervous  pathway  becomes  so  deeply 
cut  that,  given  a  certain  incoming  impulse,  the  resulting 
nervous  discharge  can  make  its  progress  outward  by  that 
course  alone  which  lias  been  prepared  for  it  by  permitting 
previous  impulses  to  pass  that  way.  Then  a  habit  has 
become  "fixed,"  and  we  all  know  how  difficult  it  is  to 
change  a  fixed  habit. 

We  have  already  seen  how  the  possibility  of  acquiring 
habits  relieves  the  brain  of  the  necessity  of  attention  to 
many  of  the  movements  of  the  muscles  and  vastly  increases 
the  number  of  things  which  one  can  do.  Most  of  us  estab- 
lish in  time  an  order  of  proceeding  for  the  daily  processes 
of  dressing  and  undressing,  for  example,  so  that  we  go 
through  them,  day  after  day,  in  a  certain  routine  without 


HYGIENE   OF   THE   NERVOUS   SYSTEM  323 

giving  any  particular  thought  to  them,  and  perhaps  with- 
out knowing  that  we  do  make  the  necessary  movements 
in  the  same  succession,  time  after  time.  In  such  a  case 
the  first  muscular  contraction  (as,  for  instance,  the  first 
voluntary  motion  after  we  have  decided  to  retire  to  rest) 
is  the  setting  in  motion  of  a  chain  of  events,  each  of  which 
follows  without  thought  from  the  sensation  of  the  pre- 
ceding muscular  contraction.  To  change  the  order  of  the 
movements  costs  a  definite  effort,  as  when  we  decide  for 
some  reason  to  put  on  or  off  the  left  shoe  first,  when  we 
have  formed  a  habit  of  putting  on  or  off  the  right  one 
first. 

469.  Character.  —  It  is  the  habits  acquired  which  deter- 
mine character.  What  a  man  has  made  himself  by  the 
time  he  is  twenty-five  or  thirty  years  of  age,  through  the 
pathways  formed  in  the  plastic  substance  of  his  brain, 
such  he  is  almost  sure  to  remain  to  the  end  of  life.  In 
many  cases  habits  are  by  that  time  so  strong  that  they 
cannot  be  changed.  The  brain  seems  to  have  become  har- 
dened, "  set,"  so  that  new  channels  for  nervous  impulses 
can  no  longer  be  made.  Even  earlier  in  life  many  habits 
of  daily  practice  have  usually  become  unchangeably 
formed.  The  methods  of  speech,  especially  the  idioms  of 
ordinary  conversation,  for  one's  whole  life,  are  those  ac- 
quired in  childhood.  A  man  may  become  learned,  pol- 
ished, and  scholarly  in  prepared  or  written  productions 
while  still  retaining  in  daily  familiar  speech  rude  and 
uncultivated  expressions  learned  in  early  years.  It  would 
be  too  much  to  say  that  even  fixed  habits  cannot  be 
changed,  but  to  accomplish  a  change  requires  an  amount 
of  determination  and  persistence  not  common  among  men. 

470.  To  build  into  the  material  substance  of  the  nerv- 
ous system  a  tendency  to  do  right  and  wise  acts  in  the 


324  THE   NERVOUS    SYSTEM 

best  way,  to  think  pure  and  unselfish  thoughts,  to  cherish 
the  loftiest  and  noblest  aspirations,  is  the  most  important 
business  of  youth.  Manhood  prepared  by  such  training  is 
ready  for  grand  achievements.  The  spinal  cord  and  the 
lower  brain  centers  have  been  drilled  to  prompt  and  accu- 
rate reflex  action,  and  much  of  the  mechanical  labor  of 
life  is  left  to  their  unconscious  ordering.  Not  only  are 
the  ordinary  movements  of  the  body  in  walking,  riding, 
and  the  various  athletic  sports  thus  directed,  but  facility 
and  correctness  of  speech,  both  oral  and  written,  have  be- 
come no  longer  matter  for  cerebral  care.  Rapid  writing, 
attended  by  accuracy  in  respect  to  the  accepted  forms  and 
rules  of  composition,  has  been  acquired  by  thorough  train- 
ing, and  the  brain  is  left  free  to  concentrate  all  its  powers 
upon  the  higher  activities  of  thought  and  imagination. 
That  the  products  of  those  activities  shall  be  worthy  is 
determined  by  the  abundant  store  of  memories  of  worthy 
and  beautiful  objects,  acts,  purposes,  and  thoughts.  No- 
ble deeds  will  be  inevitable  because  of  the  constantly 
repeated,  voluntary  turning  of  nervous  impulses  into 
channels  for  such  results.  Acts  demanded  by  great  and 
sudden  emergencies,  when  deliberation  and  reason  are 
impossible,  will  be  unselfish,  wise,  and  every  way  worthy, 
because  previous  voluntary  action  has  habituated  all  the 
nerve  centers  so  to  respond  to  stimuli  received  when  judg- 
ment and  reason  have  had  time  to  consider. 

471.  Heredity.  —  Did  each  individual  come  into  the 
world  with  all  his  powers  in  their  normal  condition,  and 
grow  up  in  the  most  favorable  surroundings,  such  sym- 
metrical and  perfect  manhood  might  be  the  expected  and 
ordinary  result.  Unhappily  that  is  not  the  case.  Many 
eminent  men  of  science  believe  that  the  impressions  made 
upon  the  soft  substance  of  a  man's  brain  in  early  life  are 


HYGIENE   OF   THE   NERVOUS   SYSTEM  325 

SO  deep  and  lasting  that  they  not  only  persist  through- 
out the  individual  life,  but  also  affect  the  brains  and 
nerves  of  his  children,  and  his  children's  children,  so 
that  they  may  have  from  their  birth  tendencies  to  act 
as  their  parents  or  their  grandparents  have  been  accus- 
tomed to  act.  They  inherit  a  certain  kind  of  nervous  tem- 
perament, Ave  say,  and  their  nerve  cells  have  a  natural 
readiness  to  respond  in  certain  ways  to  the  influences 
which  come  to  them.  This  may  be  a  powerful  aid  to  the 
development  of  upright  and  noble  character,  and  it  may 
.be  an  almost  irresistible  force  urging  in  the  opposite  direc- 
tion. It  has  been  observed  in  many  cases  that  the  chil- 
dren of  criminals  become  criminal  for  generation  after 
generation.  The  inherited  hent  of  their  minds  appears  to 
be  evil,  and  as  a  rule  their  surroundings  and  associations 
are  also  evil.  The  power  of  a  bad  inheritance  may,  how- 
ever, be  neutralized  by  a  good  environment. 

472.  Influence  of  Alcohol  on  the  Nervous  System.  —  While 
the  excessive  use  of  alcoholic  drinks  works  injury  to  every 
part  of  the  body,  it  is  largely  through  the  direct  effect  of 
alcohol  upon  nervous  tissue  that  the  various  evils  are 
accomplished. 

We  will  consider  the  physiological  influence  of  alcohol 
on  the  nervous  system  under  two  heads :  (1)  acute  dis- 
eases caused  hy  alcohol;  (2)  chronic  diseased  conditions. 
Afterward  the  moral  effects  will  receive  attention. 

473.  Dipsomania  (an  acute  disease)  is  the  name  given  to 
the  morbid  craving  for  alcohol  which  renders  a  person 
utterly  irresponsible  for  his  acts  while  engaged  in  the  mad 
pursuit  of  that  which  he  believes  will  satisfy  his  consuming 
thirst.  It  is  a  distinctly  diseased  condition  of  the  nervous 
system,  and  may  result  from  what  is  only  a  slightly  ex- 
cessive use  of  alcoholic  liquors  by  the  sufferer  himself,  or  it 


326  THE   NERVOUS   SYSTEM 

may  be  due  to  a  diseased  state  of  nervous  tissue  inherited 
from  an  ancestor  accustomed  to  such  use,  though  he  may 
never  have  indulged  to  the  extent  of  intoxication.  This 
form  of  alcoholism  is  now  considered  and  treated  as  a  dis- 
ease by  medical  rather  than  moral  methods. 

474.  Another  acute  form  of  alcoholism  is  called  delirium 
tremens,  and  this  is  so  terrible  to  witness,  so  frightful  to 
suffer,  that  men  speak  the  very  name  with  bated  breath. 
It  occurs  in  persons  whose  nervous  systems  have  been  for 
a  considerable  time  under  the  poisonous  influences  of 
excessive  amounts  of  alcohol.  At  the  height  of  the 
attack  the  patient  becomes  a  raving  maniac,  subject  to 
the  most  torturing  illusions  and  sometimes,  with  the 
unnatural  strength  of  madness,  overpowering  and  escap- 
ing from  several  attendants.  Repeated  recurrence  of  the 
disease  is  almost  certain  to  be  fatal,  though  the  first  attack 
is  rarely  so.     Permanent  insanity  may  precede  death. 

475.  Chronic  Diseased  Conditions  arise  from  the  gradual 
poisoning  of  the  system  by  the  continued  use  of  beverages 
containing  alcohol.  Even  though  we  admit  that  alcohol 
in  a  definite  small  amount  is,  in  some  cases  at  least,  fully 
oxidized  in  the  body,  like  other  carbohydrates,  and  so 
supplies  energy  as  food,  we  must  never  forget  that  differ- 
ent constitutions  may  be  differently  affected,  and  condi- 
tions as  to  climate,  temperament,  and  habits  of  life  may 
cause  variations  in  its  influence  upon  health  and  character. 
We  can  never  know  perfectly  the  nature  of  all  the  innu- 
merable strains  of  hereditary  tendency  which  unite  to  make 
an  individual  what  he  is.  Some  one  of  these  may  have 
impressed  upon  the  nerve  cells  an  instability,  a  weakness, 
a  peculiar  susceptibility  to  the  influence  of  alcohol,  so  that 
the  first  taste  may  arouse  the  insatiable  craving  which 
leads  to  dipsomania.    In  another  case,  the  inherited  weak- 


HYGIENE   OF   THE   NERVOUS   SYSTEM  327 

ness  may  render  the  child  of  an  inebriate  an  epileptic,  an 
imbecile,  or  a  consumptive.  We  can  never  foresee  just 
how  the  transmitted  nervous  weakness  will  manifest  itself, 
but  as  a  rule  the  descendants  of  those  whose  systems 
are  poisoned  by  alcohol  are  enfeebled  in  body  or  mind  or 
both. 

476.  But  suppose  a  man  to  have  derived  from  his  ances- 
tors a  sound  constitution  and  to  have  become  addicted 
to  the  moderate  use  of  alcohol;  the  insidious  nature  of 
the  dangerous  substance  may  gradually  lead  him  to  con- 
sume, insensibly  perhaps,  only  a  little  more  than  the  cells 
can  oxidize.  Without  realizing  it,  he  may  slowly  poison 
his  system.  The  primary  effect  is  upon  the  brain  ;  there 
is  congestion  and  overexcitement  of  the  nerve  cells  there — 
conditions  which  gradually  extend  to  the  nerve  cells  of  the 
spinal  cord  ;  inflammation  sets  in,  and  there  follows  fibrous 
degeneration  of  the  tissues,  substituting  an  inferior  form 
for  the  specialized  tissues  which  do  the  work  of  the  organs 
in  various  parts  of  the  body.  Paralysis  ma}^  result,  or  epi- 
lepsy, or  dyspepsia  from  lack  of  the  due  amount  of  nerv- 
ous influence  upon  the  digestive  organs,  or  any  one  of  a 
thousand  forms  of  disorder,  some  of  which  have  been  men- 
tioned in  preceding  chapters.  Though  a  man  may  never 
drink  to  intoxication,  and  never  realize  that  he  is  using 
alcohol  to  excess,  he  may  nevertheless  become  seriously 
diseased  in  consequence  of  his  moderate  indulgence, 
or  what  he  believes  to  be  such,  while  wondering  why 
he  is  not  well  and  strong.  Still  less  does  he  consider 
the  legacy  of  evil  which  he  may  be  laying  up  for  his 
children. 

Life  insurance  companies  have  gathered  an  immense 
body  of  statistics  respecting  human  life,  with  sole  refer- 
ence to  their  bearing  upon  the  business  of  insurance,  and 


328  THE   NERVOUS   SYSTEM 

it  is  well  known  that  life  insurance  companies  regard 
policies  upon  the  lives  of  drinking  men  —  even  "  moder- 
ate drinkers  "  —  as  involving  "  extra  risk."  Their  figures 
have  convinced  them  that  the  man  who  uses  no  alcoholic 
beverages  is  likely  to  live  longer  than  one  who  does. 

477.  Many  believe  that  climate  has  much  to  do  with 
the  influence  of  alcohol  on  the  nervous  system.  Our 
American  climate  is  peculiarly  stimulating  to  the  nerves, 
and  our  systems  are,  in  consequence,  less  able  to  bear  the 
additional  stimulation  of  exciting  beverages,  while  the 
narcotic  effects  take  place  more  readily  than  in  other 
climates,  and  self-control  is  more  easily  overthrown.  This 
is  another  reason,  to  us,  for  shunning  the  acquisition  of 
the  alcohol  habit. 

The  influence  of  race  has  also  to  do  with  the  prevailing 
use  of  strong  drink  and  its  evil  effects.  The  Teutonic 
peoples  are  recognized  as  especially  susceptible  to  the 
taste  for  intoxicants,  perhaps  because  of  their  eager  crav- 
ing for  excitement,  for  action,  for  enterprise  ;  and  because 
of  that  very  craving  they  can  indulge  with  less  safety  the 
appetite  for  stimulants. 

478.  The  Moral  Effects  of  Alcoholic  Poisoning  concern  the 
individual  himself,  his  family  and  friends,  and  the  whole 
community  of  which  he  is  a  member. 

The  struggle  of  life  grows  more  intense  the  world  over ; 
competition  in  all  lines  of  effort  is  keener ;  success  is  more 
difficult.  Every  one  has  need  of  all  his  powers  of  mind 
and  body  at  their  highest  possible  level  of  efficiency.  A 
man  engaged  in  business  needs  every  day  and  hour  the 
use  of  the  very  best  and  most  careful  judgment,  lest  a  false 
step  —  the  buying  of  goods  at  the  wrong  time,  the  selling 
at  the  wrong  price,  a  mistake  as  to  quality  or  style,  a 
wrong   estimate   of  the   tendency  of   the  market  —  may 


HYGIENE    OF   THE   NERVOUS   SYSTEM  329 

give  his  competitors  an  advantage  and  lead  to  his  own 
ruin.  In  the  professions  it  is  no  less  true  that  no  man 
should  dare  run  the  risk  of  befogging  his  judgment.  A 
physician  known  to  be  a  tippler  will  lose  the  best  prac- 
tice ;  the  lawyer  whose  legal  advice  is  sometimes  cloudy, 
because  of  a  trifle  too  much  alcohol  in  his  morning  dram, 
will  not  command  the  confidence  of  those  wishing  counsel. 

A  man  seeking  employment  is  likely  to  be  met  at  every 
turn  by  questions  as  to  his  habits  respecting  beverages 
containing  alcohol  and  his  use  of  tobacco.  Several  of  the 
great  railroad  corporations  employ  only  total  abstainers 
in  any  capacity.  Purely  from  pecuniary  considerations 
they  cannot  afford  to  run  the  risk  of  accident  upon  their 
roads,  —  involving  destruction  of  the  property  of  the  road, 
with  also  many  thousands  of  dollars  to  pay  for  life  and 
limb  destroyed,  —  because  perhaps  a  brakeman,  having 
taken  a  "  drop  too  much,"  was  a  little  uncertain  in  his 
vision  and  did  not  grasp  as  quickly  as  usual  the  meaning 
of  the  signals ;  or  because  a  telegraph  operator  had  fud- 
dled his  brain  with  beer  and  had  forgotten  to  send  the 
dispatch  which  would  have  prevented  a  frightful  wreck. 
So  in  respect  to  positions  in  the  great  commercial  houses 
where  trustworthiness,  alertness,  stability  of  character, 
are  required ;  —  it  is  those  who  drink  neither  brandy  nor 
beer  who  stand  the  best  chance,  other  things  being  equal, 
of  securing  desirable  positions.  In  practically  every  walk 
of  life  a  man  is  handicapped  in  the  race  if  he  is  believed 
to  be  a  drinking  man. 

All  these  facts  clearly  indicate  the  opinion  of  the  world 
in  general  that,  considered  merely  as  a  piece  of  mecha- 
nism for  accomplishing  various  sorts  of  work,  a  man 
who  takes  no  alcohol  into  his  machine  is  worth  more  than 
one  who  does ;  so  that  a  man  who  drinks  thereby  deliber- 


330  THE  NEKVOUS   SYSTEM 

ately  lowers  his  own  money  value  to  the  world  and  to 
himself. 

479.  But  there  are  higher  considerations  than  these. 
Alcohol  in  small  quantities  stimulates  the  cells  to  vig- 
orous action  for  a  time ;  then  reaction  and  weakness  may 
follow.  In  larger  quantities  alcohol  produces,  instead 
of  a  stimulating  effect,  a  narcotic  poisoning  which  par- 
alyzes the  nerves.  This  is  first  apparent  in  the  higher 
cerebral  centers,  and  if  the  poison  is  sufficient  in  amount, 
the  paralysis  extends  till  the  whole  voluntary  portion  of 
the  nervous  system  is  involved,  leaving  only  the  centers 
controlling  the  vital  functions  unaffected.  The  first 
glass  of  liquor  may  simply  render  a  man  unusually  lively, 
talkative,  perhaps  brilliant,  eloquent,  entertaining,  con- 
fidential, speaking  freely  of  private  affairs,  revealing 
secrets.  This  stage  will  pass  away  before  long,  and  if 
another  glass  is  taken,  and  another,  a  progressive  par- 
alyzing of  the  mental  faculties  is  seen.  The  ready  flow 
of  language  disappears,  utterance  becomes  thick,  and  ideas 
confused,  stupor  comes  on,  and  the  man  falls  to  the  floor 
"dead  drunk,"  though  circulation  and  respiration  still 
go  on.  If  he  has  taken  alcohol  enough^  these  too  will 
cease,  from  the  paralysis  of  the  vital  centers,  and  the 
victim  will  die.  Occasionally  a  man  runs  through  this 
course  in  a  single  debauch,  but  such  cases  are  rare. 
Usually  years  of  progressive  deterioration  precede  the 
great  catastrophe.  The  man's  friends  look  on  in  help- 
less anguish.  Noble  manhood  gradually  sinks  to  the 
level  of  the  beast,  and  below  even  that.  He  who  was 
designed  to  be  a  mighty  power  for  good  to  himself  and 
to  the  world,  becomes  a  curse  to  himself,  a  disgrace  and 
a  terror  to  his  family  and  a  burden  to  the  community, 
which  must  employ  police  to  watch  him,  build  a  hospital 


HYGIENE   OF  THE   NERVOUS   SYSTEM  331 

or  a  prison  to  receive  him,  and  must  finally  bury  him  at 
public  expense  and  care  for  his  unfortunate  family. 
How  is  it  that  a  being  endowed  with  reason  can  deliber- 
ately put  an  enemy  into  his  mouth  to  steal  away  his 
brains,  and  ruin  body  and  soul  ? 

Because  one  man  whom  we  chance  to  know  drinks 
daily  a  small  quantity  of  wine  or  beer,  and  does  not 
acquire  that  craving  for  more  which  leads  to  drunken- 
ness, nor  apparently  injure  himself  in  any  way  thereby, 
it  is  never  safe  to  conclude  that  another  man  can  do  like- 
wise. Nothing  is  more  uncertain.  At  the  same  time  it 
is  a  fact  of  common  observation  which  no  one  will  deny, 
that  multitudes  make  shipwreck  of  manhood  every  year 
through  the  excessive  use  of  alcohol ;  yet  no  one  of  them 
expected  to  be  more  than  a  "  moderate  drinker,"  not  one 
but  would  have  scorned  the  suggestion  that  he  might  in 
time  become  the  vile  drunkard  of  the  gutter. 

480.  There  is  one  infallible  way  of  escaping  these  ills, 
and  there  is  but  one.  That  is  to  abstain  wholly  from 
alcoholic  beverages.  It  is  also  a  harmless  way ;  it  can 
do  injury  to  no  one.  While  it  insures  a  man  against  the 
frightful  evils  of  drunkenness,  this  course  also  makes  it 
possible  that  by  the  force  of  his  example  he  may  help 
many  a  weak,  tempted  fellow-man  to  escape  the  seduc- 
tions of  the  wine  cup. 

It  may  be  an  admirable  thing  for  a  man  to  be  able  to 
exercise  the  judgment,  the  self-restraint  which  permits 
him  to  indulge  his  appetite  for  alcohol  to  exactly  that 
extent  only  which  he  believes  to  be  harmless  or  helpful 
to  himself,  never  yielding  to  a  temptation  to  exceed  the 
self-imposed  limit.  Is  it  not  yet  more  admirable  for  a 
man  to  recognize  the  weakness  of  human  nature,  and  the 
possibility  —  shown  every  year  by  thousands  of  sorrowful 


332  THE  NERVOUS   SYSTEM 

instances  —  that  even  the  manhood  which  seems  strongest 
may  be  overcome,  and  so  refuse  to  take  the  fearful  risk  of 
placing  himself  within  the  power  of  so  insidious  a  foe  ? 
Does  not  the  truest  courage  lead  a  man  to  avoid  ventur- 
ing needlessly  and  recklessly  into  the  presence  of  so  terri- 
ble a  danger  ?  And  should  not  a  man  of  really  noble 
character  deliberately  choose  to  make  his  influence  help- 
ful, rather  than  harmful,  to  those  weaker  than  himself  ? 

481.  Other  Narcotics  in  Common  Use.  —  Narcotics  are  very 
widely  used  by  the  human  family  for  the  relief  which 
they  give  from  pain  or  fatigue,  or  for  the  direct  pleasur- 
able sensations  which  they  impart.  All  are  deadly  poisons 
when  taken  in  sufficient  quantities.  Those  most  common 
(after  alcohol)  are  tobacco  and  opium. 

It  has  already  been  shown  that  tobacco  may  affect 
unfavorably  many  parts  of  the  system,  and  is  especially 
injurious  to  the  young.  It  stimulates  in  small  quantities 
and  narcotizes  in  larger  ones,  working  its  effects  directly 
upon  the  nervous  system.  Nicotine  is  a  powerful  poison 
found  in  tobacco.  It  affects  the  nerve  cells,  injures  the 
brain,  and  leads  especially  to  weakness  of  the  heart  by 
interfering  with  its  supply  of  nervous  force.  Many 
cases  of  cancer  of  mouth  and  throat  are  believed  to 
have  resulted  from  tobacco  smoking. 

Opium^  for  its  benumbing  influence  upon  the  nerves,  is 
used  by  large  numbers  of  persons,  especially  in  Oriental 
lands.  Its  continued  use  deranges  all  the  digestive  proc- 
esses, disorders  the  brain,  and  weakens  and  degrades  the 
character.  Like  alcohol,  it  produces  an  intolerable  crav- 
ing for  itself,  and  the  strongest  minds  are  not  proof 
against  the  deadly  appetite. 

482.  Self-control  versus  Appetite.  —  Man  is  a  bundle  of 
appetites.     Every  organ,  every  cell  even,  craves  its  appro- 


HYGIENE   OF   THE   NERVOUS   SYSTEM  333 

priate  stimulus.  Animals  under  natural  conditions  gratify 
the  appetites  as  they  arise  only  to  that  extent  which  is 
healthful  for  the  whole  body.  Man  alone,  whose  highly 
developed  brain  is  overlord  to  the  rest  of  his  system,  per- 
mits an  unwholesome  indulgence  of  appetite  to  interfere 
with  this  general  well-being.  Alcohol,  opium,  and  their 
like  are  far  from  being  the  only  substances  whose  excess- 
ive use  injures  the  organism  and  degrades  character. 
Children  are  often  allowed  to  indulge  a  natural  fondness 
for  sweets  to  an  extent  which  is  ruinous  to  disrestion  ; 
for  sugar,  which  is  a  useful  and  necessary  food  in  suitable 
quantities,  becomes  in  larger  ones  a  poison  to  the  system. 
Boys  pampered  with  dainties  from  infancy  logically  infer 
that  a  fancy  for  cigars  or  beer  may  be  similarly  gratified. 
Appetite  for  even  the  most  wholesome  food  may  be  in 
excess  of  bodily  needs,  and  the  practice  of  gluttony  is 
certain  to  derange  nutrition. 

A  child  should  be  early  taught  that  because  he  "  likes  " 
a  certain  article  of  food  he  should  not  therefore  continue 
to  eat  it  after  natural  hunger  is  satisfied,  or  at  times  when 
he  does  not  need  food ;  while  to  persist  in  eating  or 
drinking  that  which  experience,  or  the  advice  of  those 
competent  to  judge,  has  taught  him  to  be  harmful,  should 
be  regarded  as  unworthy  a  rational  being. 

These  are  but  illustrations  of  the  manifold  forms  of 
intemperance  Avhich  work  untold  harm  to  the  physical 
and  moral  natures.  There  seems  no  possibility  of  im- 
provement to  our  race  except  as  the  young  are  led  to 
recognize  the  manliness  and  dignity  of  controlling  one's 
appetites. 

483.  And  it  is  not  in  respect  to  the  delights  of  the 
palate  .only  that  a  foolish  self-indulgence  prevails.  The 
love    of   selfish  pleasure   in  any  form  may  be  developed 

macy's  piiys.  — 21 


334  THE  NERVOUS   SYSTEM 

till  it  encroaches  upon  the  general  well-being.  Man's 
reason  was  designed  to  dominate  all  the  appetites,  to 
gratify  them  only  so  far  as  will  conduce  to  the  best  use 
of  the  higher  capacities.  If  the  mind  does  not  rule  and 
restrain  the  appetites  by  the  dictates  of  reason,  then  the 
body  and  not  the  mind  is  on  the  throne,  and  man  sinks 
to  the  level  of  the  beasts  that  perish.  Temperance  in  all 
things,  a  wise  moderation  according  to  reason  and  expe- 
rience, subordination  of  the  appetites  and  passions  of  the 
physical  being  to  the  nobler  requirements  of  the  spiritual 
nature,  and  to  the  still  finer  sentiment  of  unselfish  conse- 
cration of  all  one's  powers  to  the  service  of  humanity  — 
these  are  the  principles  which  dominate  the  highest  type 
of  manhood. 


PART  y 

THE   PRESERVATION    OF   HEALTH 

CHAPTER   XXIV 
HEALTH  AND  DISEASE 

484.  Health,  in  man,  is  that  condition  of  the  organism 
in  which  all  the  various  parts  composing  it  perform  their 
functions  perfectly,  so  that  the  largest  amount  of  the  best 
work  of  which  the  being  is  capable  is  performed  easily 
and  without  discomfort.  Health  is  attended  with  a  feel- 
ing of  buoyancy,  vigor,  and  happiness.  Disease  is  the 
result  of  disordered  action  in  some  one  or  more  parts  of 
the  organism,  usually  long-continued  and  affecting  more 
and  more  the  various  vital  processes. 

Many  of  the  ways  in  which  persons  are  accustomed  to 
injure  the  health  by  inattention  to  hygienic  rules,  or  by 
violations  of  them,  have  been  alluded  to  in  preceding 
chapters.  Incorrect  habits  of  life  are  the  direct  cause  of 
many  diseases,  and  indirectly  cause  many  more  by  weak- 
ening the  organs,  and  preparing  the  system  to  yield 
readily  when  exposed  to  the  influences  of  specific  disease. 

485.  Bacteria.  —  It  is  now  known  that  several  forms  of 
disease  arise  from  the  growth  and  multiplication,  within 
the  body,  of  certain  microscopic  forms  of  life  called  bac- 
teria, or  bacilli,  or  microbes,  or  germs.     These  are  living 

335 


336  THE   PEESERVATION   OF   HEALTH 

cells  belonging  to  the  lowest  orders  of  plants.  They  pos- 
sess the  power  of  rapid  increase  by  repeated  division  of 
the  cells,  so  that  many  millions  may  be  produced  in  a 
short  time  from  a  single  one.  They  are  propagated  also 
by  means  of  very  minute  spores,  which  may  float  in  the 
air,  mix  with  the  dust  of  a  street  or  a  room,  or  cling  to 
walls,  clothing,  or  furniture.  Only  moisture,  warmth, 
and  albumin  for  food  are  needed  for  their  growth.  Prob- 
ably most  (perhaps  all)  of  these  tiny  organisms  have  some 
useful  part  to  play  in  the  infinitely  varied  operations  of 
nature;  but  a  few  varieties  are  known  to  be  enemies  to 
human  life  and  health.  Certain  sorts  of  bacteria  are 
always  concerned  in  the  putrefaction  of  organic  matter, 
that  is,  as  they  multiply  they  break  up  the  complex  com- 
pounds in  vegetable  and  animal  substances,  and  reduce 
them  to  simpler  chemical  forms  which  may  again  be  used 
as  food  for  plants.  Thus  dead  animal  and  vegetable  mat- 
ter is  being  constantly  oxidized  by  the  bacteria  found 
everywhere  in  the  soil,  and  rendered  fit  again  to  support 
life.  In  this  they  of  course  minister  to  man's  welfare, 
although  the  process  of  decay  is  attended  by  the  pro- 
duction of  deadly  poisons,  which  may  enter  the  body  and 
cause  disease. 

486.  Bacteria  within  the  Body.  —  The  dry  speck  of  dust 
which  is  the  spore,  or  germ,  of  a  disease  may,  while  it 
remains  dry,  exist  for  an  uncertain  number  of  years  as  an 
inert,  harmless  bit  of  matter.  It  may  be  subjected  for 
weeks  to  cold  many  degrees  below  zero,  and  even  for  a 
short  time  to  heat  above  that  of  boiling  water,  without 
destruction  of  its  vitality.  It  may  then  fall  upon  a  moist 
bit  of  albumin  in  the  air  passages  of  a  man,  or  in  the 
alimentary  canal,  or  in  blood  or  lymph  through  a  broken 
surface,  grow  with  wonderful  rapidity,  and  swiftly  poison 


HEALTH   AND   DISEASE  337 

the  whole  body.  The  dangerous  germ  may,  indeed,  be 
caught  by  the  moist  surface  of  the  mucous  membrane  and 
removed  before  it  has  done  harm;  for  it  is  one  of  the 
functions  of  the  moist  lining  of  the  winding  nasal  passages 
to  strain  out  the  irritating  and  disease-bearing  particles 
from  the  air,  and  the  ciliated  epithelium  of  the  lower 
air  passages  also  affords  protection  in  the  same  way. 
Expired  air  is  practically  free  from  germs  and  other  dust. 
What  we  call  "  taking  cold  "  is  now  believed  to  be  due  to 
the  poisonous  action  of  bacteria  fastening  upon  the  mucous 
membrane  where  the  cells  have  been  injured  by  cold  or 
in  some  other  manner.  Finding  food  at  the  injured  spot, 
the  bacteria  multiply  and  cause  inflammation  of  the  air 
passages  and  general  discomfort,  sometimes  resulting  in 
disease. 

487.  It  has  been  found  that  a  large  number  of  bacteria 
of  several  varieties  are  always  present  in  the  human  mouth. 
The  saliva  has  the  power  of  destroying  a  limited  number 
of  the  harmful  kinds,  but  others  remain  to  multiply. 
Certain  sorts  cause  decay  of  the  teeth  (where  the  enamel 
is  defective).  Others  may  make  their  way  into  the  lungs 
or  the  stomach.  As  they  grow  they  manufacture  from 
the  albumin  which  they  decompose,  certain  poisons,  called 
toxins.  These  may  enter  the  circulation  and  carry  the 
deadly  influence  to  all  parts  of  the  system.  If  the  stomach 
is  healthy  and  the  gastric  juice  normal,  many  dangerous 
germs  will  be  destroyed  in  the  stomach.  It  is  even  shown 
by  experiment  that  those  of  cholera  and  typhoid  fever  are 
quickly  killed  by  the  gastric  juice.  Other  germs  have 
greater  resisting  power  and  are  able  to  multiply  in  the 
stomach,  causing  dyspeptic  symptoms  or  specific  disease. 
Some  forms  of  bacteria  feed  upon  and  destroy  other  forms. 
Many  sorts  escape  the  destructive  action  of  other  germs 


338  THE  PRESERVATION  OF   HEALTH 

and  of  the  digestive  juices,  and  reach  the  intestines  to 
develop  there.  Still  other  kinds  are  always  normally 
present  there.  Immense  numbers  are  always  found  in 
the  contents  of  the  large  intestine.  The  bile,  which  is 
known  to  have  the  power  of  preventing  putrefaction, 
appears  to  be  able  to  modify  the  action  of  the  microbes  and 
to  keep  that  action  within  certain  limits  which  may  render 
it  helpful  to  digestion. 

Taken  in  through  a  wound  in  the  epithelium,  the  noxious 
germs  cause  inflammation  and  swelling,  and  their  toxins 
may  circulate  through  the  body.  Or  by  the  wonderful 
power  of  the  white  corpuscles  of  the  blood,  which  feed 
upon  the  bacteria  in  the  blood,  the  evil  may  be  neutralized. 
The  plasma  of  blood  and  lymph  seems  also  to  possess  the 
property  of  destroying  certain  toxins,  or  of  protecting 
the  system  from  their  action. 

488.  Antitoxins.  —  In  recent  years  some  marvelous  dis- 
coveries have  been  made  respecting  nature's  way  of  coun- 
teracting in  the  body  the  effects  of  certain  germs  of 
disease. 

It  has  been  shown  that  in  the  progress  of  certain  in- 
fectious or  contagious  diseases  there  is  developed  in  the 
serum  of  the  blood  or  in  the  tissues  a  substance  which 
is  a  poison  to  the  bacteria  causing  the  disease,  or  a  sub- 
stance which  neutralizes  the  toxins  produced  by  them. 
In  course  of  time  —  it  may  be  days  or  weeks  —  enough  of 
this  substance,  called  antitoxin^  is  manufactured  to  neu- 
tralize the  toxin  or  to  destroy  the  germs  of  the  particular 
disease,  and  the  patient  recovers.  In  certain  cases,  as  in 
measles,  smallpox,  whooping  cough,  etc.,  this  protecting 
substance  seems  either  to  remain  in  the  blood  or  to  be 
continually  produced  for  the  rest  of  life,  giving  perma- 
nent security  from  the  disease.     In  others,  such  as  diph- 


HEALTH  AND   DISEASE  339 

theria  and  pneumonia,  the  security  given  by  the  antitoxin 
is  only  temporary. 

Certain  animals  are  known  to  be  subject  to  some  of  the 
same  diseases  which  attack  human  beings,  or  to  be  suscepti- 
ble to  them  when  the  particular  poisons  are  introduced  into 
their  systems.  Other  animals  cannot  be  made  to  "  take  " 
certain  infectious  diseases,  even  when  the  specific  germs 
and  toxins  are  injected  into  their  circulations.  They  are 
said  to  be  "  naturally  immune  "  to  those  diseases,  that  is, 
an  antitoxin  is  supplied  by  nature  in  their  blood  serum 
for  the  germs  or  toxins  of  those  diseases.  Other  animals 
are  rendered  immune  to  certain  diseases  by  having  experi- 
enced them. 

Advantage  has  been  taken  of  this  knowledge  respecting 
animals  for  the  benefit  of  man.  In  several  cases  the  anti- 
toxic substances  in  the  blood  of  animals  immune  to  cer- 
tain diseases  have  been  separated  out  and  injected  in 
minute  quantities  into  the  veins  of  human  subjects  suffer- 
ing from  the  particular  infection.  The  proportion  of 
recoveries  when  the  antitoxins  are  used  under  proper 
safeguards  is  increasingly  and  encouragingly  large. 

489.  Vaccination  for  smallpox  was  the  first  great  dis- 
covery in  this  direction.  By  means  of  it  smallpox,  which 
was  once  the  great  scourge  of  the  human  race,  —  as  com- 
mon as  measles  or  whooping  cough  is  now,  —  has  become 
comparatively  rare.  The  use  of  the  diphtheria  antitoxin, 
which  is  derived  from  the  blood  serum  of  a  horse  which 
has  been  innoculated  with  the  diphtheria  germ,  is  fast 
becoming  general,  and  we  may  hope  to  see  diphtheria  — 
that  terror  of  childhood  —  disappear  with  the  advance 
of  beneficent  science. 

The  greatest  destroyer  of  human  life  which  now  remains 
is  consumption,  —  tuberculosis  in  its  varied  forms,  —  and 


340  THE   PRESERVATION   OF   HEALTH 

there  is  reason  to  believe  that  it  also  is  destined  to  be 
overcome  by  the  progress  of  scientific  discovery,  together 
with  a  wider  diffusion  of  sanitary  knowledge.  An  anti- 
toxin for  consumption,  called  tuberculin^  has  been  found  by 
cultivating  the  germ  obtained  from  the  mucus  raised  by 
consumptive  j^atients,  in  a  substance  found  to  favor  its 
development.  This  new  remedy  is  yet  so  recent,  and  the 
number  of  experiments  made  so  few,  that  nothing  positive 
can  be  stated  as  to  its  value.  But  there  is  good  reason  to 
hope  that  a  trustworthy  cure  for  tuberculosis  will  in  time 
be  in  common  use. 

490.  Antiseptic  Surgery  is  another  result  of  the  study  of 
the  new  science  of  bacteriology.  (^Antiseptic  is  derived 
from  two  Greek  words  meaning  "  opposed  to  putrefac- 
tion.") The  great  danger  connected  with  wounds  and 
injuries  has  been  found  to  be  due  to  the  opportunity 
which  they  give  for  harmful  germs  and  spores  to  enter 
the  system.  This  is  now  guarded  against  by  the  j)ractice 
called  sterilizing^  applied  to  all  instruments  and  appli- 
ances used  by  the  surgeon,  and  so  far  as  possible  to  the 
operating  room  itself.  The  object  is  the  destruction  of 
all  germs.  The  instruments  used  are  previously  boiled 
for  a  sufficient  time  to  kill  all  known  forms  of  life. 
Towels,  operating  gowns,  all  cloths,  dressings,  and  other 
things  used  are  sterilized  by  heat  or  antiseptic  chemicals, 
and  every  possible  precaution  is  taken  to  prevent  the 
access  of  any  bacteria  to  the  exposed  surfaces.  As  a 
consequence,  the  severest  wounds  often  heal  in  a  few 
days,  and  the  most  astonishing  operations  are  performed 
with  comparatively  slight  risk. 

491.  How  to  avert  Danger  from  Poisonous  Germs.  —  To  a 
person  in  perfect  health  it  is  probable  that  bacteria  of  all 
sorts  are  harmless.     The  healthy  stomach  seems  able  to 


HEALTH   AND   DISEASE  341 

digest  typhoid-fever  germs  as  well  as  its  natural  food. 
To  avoid  disease,  then,  we  have  but  to  keep  the  whole 
system  at  a  high  level  of  health  and  vigor.  But  few  are 
so  fortunate  as  to  possess  and  maintain  perfect  health,  and 
it  is  necessary  to  guard  against  the  entrance  of  disease 
germs  into  the  body. 

Careful  attention  to  cleanliness  of  person  and  surround- 
ings is  of  prime  importance.  The  free  use  of  soap  and 
water,  and  the  daily  cleansing  of  mouth  and  teeth,  are 
safeguards.  Many  thousands  of  bacteria  have  been 
counted  in  the  dirt  lodged  under  a  single  finger  nail, 
and  they  swarm  in  soiled  clothing.  Some  of  them  may 
be  germs  of  disease. 

All  excretions  from  diseased  persons  should  be  treated 
as  dangerous  to  health,  and  at  once  disinfected  by  fire  or 
by  other  methods  under  competent  direction.  In  cases 
of  pulmonary  consumption  or  other  diseases  of  lungs  or 
throat,  all  discharges  from  the  respiratory  passages  should 
be  received  upon  pieces  of  soft  paper  or  cloth  and  immedi- 
ately burned.  The  unseemly  practice  of  spitting  in  pub- 
lic or  in  private  places  should  be  abolished.  It  has 
undoubtedly  been  in  past  ages  an  active  cause  of  the 
spread  of  diseases  of  throat  and  lungs.  The  dried  sputum 
is  carried  hither  and  thither  by  the  air,  to  be  breathed  in 
by  unconscious  victims. 

492.  In  respect  to  cleanliness  of  dwellings  and  their 
surroundings  we  are  becoming,  year  by  year,  more  intelli- 
gent. AYe  know  that  oxygen  and  direct  sunlight  destroy 
many  harmful  germs,  and  we  are  learning  to  banish  from 
our  homes  dark  and  heavy  draperies  which  exclude  sun 
and  air  and  harbor  dust,  as  well  as  carpets  nailed  to  the 
floor  and  hence  not  easily  and  often  cleaned.  We  burn 
the  sweepings  from  our  rooms  instead  of  scattering  them 


342  THE   PRESERVATION   OF   HEALTH 

upon  the  wind,  and  do  not  allow  our  washtubs  to  be 
emptied  upon  the  ground  beside  our  door.  We  seek  as 
much  light  as  possible  for  our  cellars,  and  take  care  that 
nothing  is  left  there  to  decay.  We  look  well  to  the  source 
of  the  water  used  in  our  homes,  lest  it  should  bring  to  us 
illness  and  death,  and  we  have  a  wholesome  fear  of  "•  sewer 
gas,"  which  leads  us  to  keep  all  pipes  and  drains  well 
cleansed  and  in  good  repair. 

All  this  is  but  putting  in  practice  the  rules  of  cleanli- 
ness which  have  been  known  for  ages  to  be  necessary  to 
health.  But  we  are  now  acquainted  with  many  invisible 
and  deadly  forms  of  filth  unknown  to  our  ancestors. 

493.  Dangers  to  Health  in  Rural  Districts.  —  It  would  seem 
that  life  in  a  country  village  or  upon  a  farm,  where  every 
house  may  be  continually  surrounded  by  pure  air  and 
exposed  to  abundant  sunshine,  should  be  free  from  the 
unfavorable  influences  which  assail  dwellers  in  towns  and 
cities.  As  a  matter  of  fact,  however,  the  same  ignorance 
and  carelessness  which  are  found  in  the  city  appear  also 
in  the  country.  Sanitary  precautions  are  needed  upon  the 
farm  no  less  than  elsewhere.  How  often  do  we  know  of 
farmers'  families  suffering  from  malarial  or  typhoid  fevers, 
and  how  many  children  have  died  upon  farms  from  diph- 
theria !  Because  of  their  peculiar  advantages  country 
dwellers  are  too  often  peculiarly  careless.  Wells  for 
family  use  are  frequently  placed  where  the  leakage  from 
barnyard  or  cesspool  will  inevitably  pollute  the  water 
when  the  soil  has  become  saturated.  Even  if  the  well 
is  at  some  distance  from  all  apparent  sources  of  con- 
tamination, and  upon  higher  ground,  it  is  impossible  to 
tell  what  may  be  the  underground  conditions,  what  may 
be  the  slope  of  the  strata,  and  whether  or  not  there  is 
poisonous  leakage.     In  some  cases  the  well  is,  for  conven- 


HEALTH   AND  DISEASE  343 

ience,  very  near  the  house,  while  upon  the  ground  around 
it  is  poured  all  the  liquid  waste  of  the  household,  no  pro- 
vision being  made  for  drainage.  The  soil  then  becomes 
saturated  with  filth,  which  every  shower  washes  into  the 
well.  Sometimes  a  country  dwelling  i's  so  closely  sur- 
rounded by  trees  as  to  shut  out  the  sun  and  air  and  cause 
unhealthful  dampness.  Convenient  opportunities  for  fre- 
quent bathing  are  often  lacking,  and  in  winter  there  is 
apt  to  be  too  little  attention  to  ventilation.  With  only 
a  moderate  amount  of  intelligence  and  care,  life  in  the 
country  might  be  made  far  more  healthfuL 


CHAPTER   XXV 

COMMON   ACCIDENTS   AND   INJURIES 

494.  Surface  Wounds.  —  When  the  surface  in  any  part 
of  the  body  is  cut  or  torn,  bacteria  at  once  fasten  upon  the 
moist  parts  and  begin  their  harmful  work.  But  for  their 
presence  most  injuries  would  quickly  heal.  Nature  pro- 
vides that  the  white  cells  in  the  blood  shall  multiply 
about  the  wound  to  form  a  new  tissue.  They  also  have 
the  power  of  absorbing  and  destroying  dead  cells  and  for- 
eign matter  in  the  cut.  New  blood  vessels  grow  in  the 
injured  part  and  carry  the  material  needed  for  building 
the  new  tissue,  while  the  cells  of  the  cuticle  also  grow 
from  all  sides  to  cover  the  exposed  surface.  But  if 
poisonous  bacteria  enter  the  wound,  as  they  are  almost 
sure  to  do,  they  must  be  destroyed  by  the  white  blood 
cells  before  healing  can  take  place,  and  the  process  is 
attended  with  inflammation,  swelling,  and  pain,  besides 
being  much  prolonged.  The  edges  of  the  wound  should 
be  pressed  together  and  kept  in  place  by  bandages  or 
plasters.  Unless  foreign  matter,  such  as  sand,  glass,  or 
splinters,  is  believed  to  be  in  the  cut,  the  blood  should 
not  be  washed  away,  but  left  to  clot  and  assist  in  the 
restoration  of  the  tissues.  If  nature  is  assisted  by  the 
use  of  dressings  and  coverings  which  prevent  the  entrance 
of  bacteria,  the  cure  will  be  much  hastened. 

344 


COMMON  ACCIDENTS   AND   INJURIES 


345 


495.  Injuries  to  Blood  Vessels.  —  If  the  capillaries  merely 
are  hurt  the  blood  only  oozes  slowly  ;  a  clot  will  soon  be 
formed  and  the  healing  process  begun.  If  a  vein  is  opened, 
the  blood  flows  in  a  steady  stream  and  is  of  a  dark  purple 
color.  But  when  an  artery  is  divided,  the  blood  from  it 
is  bright  scarlet  and  comes  in  spurts,  corresponding  to  the 
heart  beats.  Bleeding  from  an 
artery  is  the  most  dangerous  and 
the  most  difficult  to  check.  That 
from  capillaries  and  small  veins 
will  ordinarily  check  itself  by 
the  formation  of  clots,  but  the 
flow  from  an  artery  may  be  so 
fast  as  to  prevent  clotting.  A 
doctor  is  usually  needed,  but  no 
time  must  be  lost  in  waiting  for 
him.  Strong  pressure  must  be 
at  once  applied  upon  the  artery, 
either  in  the  cut  or  hetiveen  the 
cut  and  the  heart.  If  the  injury 
is  to  a  limb,  a  handkerchief  or 
other  bandage  may  be  tied  (in  a 
knot  that  will  not  slip)  around 
it  above  the  hurt,  the  hard  knot 
placed  over  the  artery,  and  a  stick 

inserted  under  the  bandage  (Fig.  139).  By  twisting  the 
stick  the  knot  may  be  pressed  upon  the  artery  hard  enough 
to  stop  the  bleeding.  A  firm  hand  may  be  able  to  effect 
the  same  object  with  the  thumb  and  finger,  changing  from 
place  to  place  till  the  right  spot  is  found.  Or  a  strong 
rubber  band  or  tube  may  be  stretched,  wound  round  and 
round  the  whole  limb,  and  tied. 

A  knowledge  of  the  course  of  the  principal  arteries  is 


Fig  139.  — Manner  of  com- 
pressing an  artery  with  a 
handkerchief  and  stick. 


346 


THE   PRESERVATION  OF   HEALTH 


desirable.  That  of  the  arm  runs  in  the  middle  of  the 
inside  of  the  elbow  (Fig.  140)  and  along  the  middle  of 
the  under  side  of  the  upper  arm,  just  opposite  the  arm- 


Fig.  140.  — The  left  upper 
arm. 

The  dotted  line  indicates  the 
course  of  the  main  artery  (the 
brachial) . 


Fig.  141.— The  right  thigh. 

The  dotted  line  indicates  the 
course  of  the  main  artery  (the 
femoral) . 


pit.  In  the  leg  the  main  artery  is  in  the  middle  of  the 
hollow  behind  the  knee  and  in  the  middle  of  the  hollow 
between  the  thigh  and  the  trunk  (Fig.  141). 

496.  To  stop  bleeding  from  a  vein,  apply  pressure 
between  the  cut  and  the  extremity^  that  is,  on  the  side 
away  from  the  heart. 

Bleeding  from  the  nose  may  often  be  stopped  by  apply- 
ing cold  water,  snow,  or  ice  to  the  back  of  the  neck,  the 


COMMON   ACCIDENTS   AND    INJURIES  347 

forehead,  and  upper  part  of  the  nose.  Other  remedies  are 
to  raise  the  arms  high  above  the  head,  and  to  snuff  up  the 
nostril  a  solution  of  alum  or  other  astringent. 

497.  When  blood  comes  from  the  stomach  or  the  lungs, 
it  is  usually  a  serious  symptom,  and  calls  for  medical 
attendance.  The  patient  should  be  kept  quiet  in  bed, 
and  small  bits  of  ice  should  be  swallowed  frequently. 

Broken  Bones  and  Injuries  to  Joints.  —  See  pp.  55,  56, 
in  Chap.  IV. 

498.  Asphyxia,  or  Suffocation,  may  occur  from  various 
causes,  as  strangulation,  drowning,  the  breathing  of  cer- 
tain gases,  convulsions  which  close  the  throat,  etc.  The 
immediate  cause  is  always  a  lack  of  oxygen  in  the  lungs, 
and  fresh  air  is  always  the  remedy,  though  that  alone  is 
not  always  a  sufficient  remedy.  Artificial  respiration  is 
sometimes  necessary.  (See  §499.)  Sometimes  the  heart 
ceases  to  beat  from  an  accumulation  of  venous  blood  in 
the  right  side,  because  the  unpurified  blood  will  not  circu- 
late through  the  lungs.  In  such  a  case  the  physician 
may  draw  a  little  blood  from  a  vein,  —  after  the  air  pas- 
sages have  been  opened  and  fresh  air  supplied,  —  and  so 
start  the  circulation. 

The  most  common  cause  of  asphyxia,  except  drowning, 
is  probably  the  breathing  of  poisonous  gas  from  a  choked 
or  defective  coal  stove,  from  burning  charcoal,  or  from  a 
gas  burner.  Fresh  air,  if  supplied  in  time,  will  always 
restore,  though  the  system  may  show  symptoms  of  de- 
rangement for  days  or  weeks  afterward. 

499.  Apparent  Drowning.  —  Efforts  to  restore  persons 
apparently  dead  from  drowning  should  be  persevered  in, 
even  though  no  signs  of  life  appear  for  several  hours. 
Quickly  remove  all  clothing  from  the  upper  part  of  the 
body.     Turn  the  patient  on  his  face,  with  a  large,  hard 


348 


THE   PRESERVATION  OF   HEALTH 


roll  of  clothing  across  the  pit  of  the  stomach.  Let  the 
attendant  throw  his  own  weight  heavily  two  or  three 
times  for  a  moment  upon  the  patient's  back,  to  force  all 

the  contents  of 
the  stomach  out 
at  the  mouth. 
Gently  cleanse 
the  mouth  with 
a  handkerchief 
wrapped  round  a 

Fig.  142.  — Diagram  of  artificial  respiration,      ^nger.     ihen  im- 
showing  inspiration.  mediately  set  up 

The  arrows  show  that  the  arms  are  moved  outward  artiitcial       hredth- 
from  the  sides  of  the  chest.  .  „,  ,, 

mg,  iurn  the 
body  upon  the  back,  with  the  head  slightly  raised  and 
the  roll  of  clothing  placed  under  the  chest.  Kneel  at 
the  head,  grasp  the  arms  above  the  elbows  and  gently 
raise  them  above  the  head,  holding  them  there  two  or 
three  seconds.  Then  bring  them  carefully  down,  pressing 
them    firmly   for 

the   same  length  ..-'■"         "<., 

of  time  against 
the  sides  to  expel 
the  air.  Repeat 
these  movements 
rhythmically 
from  twelve  to 
fourteen  times   a      ^ig-  143. —Diagram  of  artificial  respiration, 

^      +]    f  showing  expiration, 

minute,  feee  that  r^^^^  arrows  show  that  the  arms  are  carried  di- 
the  tons^ue  is  rectly  forward  until  they  are  pressed  hard  against 
,  i*  1     the  chest. 

drawn      forward 

and  not  allowed  to  slip  back  to  close  the  throat.     Even 

after  signs  of  life  appear  —  often  only  as  a  faint  pinkish 


COMMON   ACCIDENTS   AND   INJURIES  349 

color  in  finger  nails  or  lips  —  continue  the  artificial  res- 
piration till  natural  breathing  is  well  established.  Keep 
the  patient  cool,  and  in  the  open  air  if  the  weather  is  not 
too  cold.  Do  not  use  the  galvanic  battery.  Dry,  warm 
clothing  must  be  provided  as  soon  as  life  appears  ;  warm 
drinks  should  be  given,  and  the  patient  will  usually  need 
to  be  kept  in  bed  for  some  days. 

500.  Other  methods  of  artificial  respiration  are  in  use. 
In  one  the  patient  is  placed  face  down,  with  a  roll  under 
the  chest,  the  head  on  one  arm.  One  person  then  gently 
rolls  the  body  upon  the  side  for  two  or  three  seconds, 
while  an  assistant  supports  the  head.  Then  the  body  is 
returned  to  the  first  position  for  two  or  three  seconds,  and 
the  movements  are  regularly  alternated  for  hours,  or  until 
natural  breathing  is  set  up. 

Even  the  forcing  of  air  into  the  patient's  lungs  from 
the  mouth  of  another  has  proved  successful,  and  one  well- 
known  method  is  to  insert  a  tube  into  the  trachea  and 
force  in  air  from  a  bellows. 

501.  Bums  and  Scalds  should  be  treated  with  great  care 
in  a  way  to  avoid  chafing  and  to  exclude  the  air.  Cold 
water  may  be  applied  immediately  to  relieve  the  pain. 
Soft  linen,  wet  in  a  very  strong  solution  of  common 
baking  soda,  or  a  thick  covering  of  wet  soda,  is  good. 
Carron  oil,  which  is  a  mixture  of  equal  parts  of  linseed  or 
olive  oil  and  lime  water,  is  an  excellent  remedy.  Vase- 
line is  useful  to  exclude  the  air.  Deep  or  extensive  burns 
or  scalds  should  have  immediate  medical  care. 

502.  A  burn  by  lye,  ammonia,  or  other  alkali  should  be 
treated  at  once  with  acid  —  dilute  vinegar  or  lemon  juice. 
A  burn  by  acid,  on  the  other  hand,  will  be  relieved  by 
applications  of  dilute  alkali,  such  as  ammonia  or  a  solution 
of  soda. 

macy's  phts.  — 22 


350  THE  PRESERVATION  OF   HEALTH 

503.  When  Clothing  takes  Fire  the  sufferer  should  lie  down 
at  once  and  roll  over  and  over  to  smother  the  flame.  Stand- 
ing up  allows  the  fire  to  reach  the  head  and  perhaps  to  be 
breathed  into  the  lungs,  while  running  fans  the  flame  and 
makes  it  spread.  A  rug  or  any  woolen  garment  at  hand 
should  be  thrown  over  the  sufferer,  care  being  taken  to 
cover  neck  and  shoulders  first,  and  so  to  force  the  fire 
downward,  away  from  the  head  and  face. 

504.  Frost  Bites.  —  Intense  cold  destroys  the  cells  of  the 
surface,  as  does  intense  heat.  Fingers,  toes,  nose,  and  ears 
are  the  parts  first  "bitten."  They  become  colorless  and 
insensible,  showing  that  the  circulation  in  the  frozen  part 
has  ceased.  Every  sort  of  warmth  must  be  avoided  till 
the  circulation  has  been  gradually  restored.  Rub  the 
chilled  parts  hard  with  snow  or  with  ice  water  until 
sensibility  and  color  return. 

Parts  which  have  been  frozen  generally  remain  particu- 
larly sensitive  to  cold.  Chilblains  often  result  from  very 
slight  exposure  and  cause  much  discomfort.  The  parts 
so  affected  should  be  bathed  often,  care  being  taken  to 
wipe  them  perfectly  dry,  and  they  should  not  be  brought 
near  a  fire,  as  heat  increases  the  irritation. 

505.  Sunstroke,  or  Thermic  Fever,  results  from  exposure 
to  extreme  heat  from  the  direct  rays  of  the  sun  or  other 
source.  Anything  which  lowers  the  vitality  of  the  body 
—  such  as  great  fatigue,  ill  health,  and  the  use  of  alcoholic 
drinks  —  helps  to  render  one  susceptible  to  the  effects  of 
high  temperatures.  When  the  air  is  stagnant  and  loaded 
with  moisture  as  well  as  very  hot,  as  it  may  be  in  close, 
confined  rooms  or  streets,  there  is  greater  danger  of  sun- 
stroke than  when  the  atmosphere  is  dry  and  circulates 
freely,  though  the  thermometer  may  stand  higher. 

A  person  suffering  from  heat  fever  is  prostrated  sud- 


COMMON  ACCIDENTS   AND  INJURIES  351 

denly,  and  usually  becomes  unconscious.  His  blood  tem- 
perature may,  in  severe  cases,  rise  to  112°,  or  even  higher, 
and  death  is  likely  to  follow  soon  unless  prompt  relief  is 
given.  The  immediate  cause  of  the  alarming  condition  is 
the  effect  of  heat  upon  the  nerve  centers  at  the  base  of 
the  brain,  which  control  respiration  and  the  circulation. 
Death  is  due  to  the  paralysis  of  those  centers. 

Treatment  consists  in  lowering  the  temperature  of  the 
body  as  rapidly  as  possible,  by  the  use  of  ice  and  very 
cold  water.  No  time  must  be  lost  in  applying  these  to 
the  whole  body,  by  means  of  Avet  sheets,  by  sprinkling 
with  the  coldest  water  at  hand,  or  by  rubbing  with  ice. 

Special  sensitiveness  to  heat  often  remains  long  after 
recovery  from  sunstroke. 

506.  Choking.  —  Small  bodies  often  stick  in  the  throat, 
and  can  neither  be  swalloAved  nor  coughed  up.  Some- 
times they  can  be  reached  with  a  finger  or  forced  out  by 
sharp  strokes  upon  the  back  between  the  shoulders,  or  by 
tickling  the  inside  of  the  throat  to  cause  vomiting.  If  a 
hard  substance  is  lodged  in  the  trachea  a  surgeon  must  be 
called  at  once. 

If  hard  objects  are  swallowed,  they  should  usually  be 
left  to  pass  off  with  rejected  portions  of  the  food,  without 
the  use  of  physic.  Bread,  cheese  and  crackers  may  be 
eaten  freely,  that  the  foreign  body  may  be  surrounded  by 
the  stiff,  pasty  material,  and  pass  easily  through  the  ali- 
mentary canal. 

507.  Foreign  Bodies  in  the  Eye.  —  Dust,  cinders,  etc.,  get 
under  the  eyelids  and  cause  much  discomfort.  As  the 
conjunctiva,  or  lining  membrane  covering  the  inside  of 
the  lids  and  the  front  of  the  eyeball,  is  one  continuous 
sheet  of  tissue,  these  particles  cannot  get  behind  the  ball 
and  can  usually  be  seen  and  removed.     Often  tlie  flow  of 


352  THE   PRESERVATION  OF   HEALTH 

tears  caused  by  the  irritation  of  the  troublesome  sub- 
stance washes  it  away,  or  it  may  be  wiped  off  by  a  fold  of 
soft  linen.  But  it  is  sometimes  lodged  far  under  one  of 
the  lids  —  usually  the  upper  one  —  where  it  is  not  so  eas- 
ily reached.  In  that  case  let  a  friend  take  the  lashes  of 
the  lid  in  the  fingers  of  one  hand  and  turn  the  lid  gently 
up  over  a  knitting  needle  or  slender  pencil  held  in  the 
other  hand  across  the  middle  of  the  lid.  Then  if  the  ball 
is  rolled  downward,  and  from  side  to  side,  the  source  of 
irritation  can  be  seen  and  removed.  Care  must  be  taken 
not  to  increase  the  inflammation  by  rubbing  the  eye. 
Applications  of  hot  water  will  give  relief  in  cases  of  slight 
inflammation. 

508.  Foreign  Bodies  in  the  Ear  are  sometimes  difficult  to 
remove.  Syringe  the  passage  gently  with  warm  water ; 
to  drive  out  insects,  drop  warm  salted  water  into  the  ear. 
If  such  efforts  do  not  avail,  no  violence  must  be  used,  but 
a  surgeon  must  be  called  in. 

509.  Foreign  Bodies  in  the  Nose. —  Small  buttons,  cherry 
stones,  peas,  beans,  etc.,  are  often  crowded  by  children 
so  far  up  the  nostrils  that  they  cannot  be  reached.  The 
child  can  sometimes  remove  such  an  object  by  "  blowing  " 
the  nose  hard,  or  it  may  be  removed  by  slapping  the 
child's  back.     Occasionally  a  surgeon  is  needed. 

510.  Sudden  Illnesses.  —  Fainting  is  directly  caused  by 
a  lack  of  blood  in  the  brain.  It  should  be  treated  by 
placing  the  patient  on  his  back  with  head  and  chest 
slightly  lower  than  the  rest  of  the  body.  Plenty  of  fresh 
air  should  be  given ;  cold  water  may  be  dashed  over  head 
and  neck.  Clothing  should  be  loosened,  and  in  severe 
cases  artificial  respiration  may  be  needed.  Strong  ammo- 
nia or  smelling  salts  applied  to  the  nostrils  is  sometimes 
useful. 


COMMON   ACCIt)ENTS   AND   INJURIES  353 

511.  Epilepsy^  or  Fits,  is  an  alarming  nervous  attack  at- 
tended by  unconsciousness  and  sometimes  by  foaming 
at  the  mouth.  It  is  a  chronic  affection,  and  has  been 
known  from  very  early  ages.  Julius  Ctesar  and  Napoleon 
Bonaparte  are  both  said  to  have  been  epileptics.  Little 
can  be  done  during  the  paroxysm  except  to  loosen  the 
clothing  and  see  that  the  sufferer  does  not  harm  himself. 
A  pad  of  cloth  crowded  between  the  teeth  will  prevent 
biting  of  the  tongue. 

512.  Hysterical  Fits  occur  oftenest  in  young  women,  and 
usually  follow  emotional  excitement.  The  patient  laughs 
and  cries,  sometimes  drops  to  the  floor,  and  disorderly, 
almost  convulsive  movements  may  take  place  ;  but  the 
tongue  is  never  bitten,  nor  does  the  patient  harm  herself. 
Dashes  of  cold  water  may  cut  short  the  attack.  Calm, 
firm,  quiet  remonstrance  from  a  strong-minded  friend 
without  much  appearance  of  sympathy  will  be  helpful. 

513.  Convulsions  in  young  children  sometimes  occur 
during  teething,  and  at  the  outset  of  some  serious 
diseases  —  as  scarlet  fever  and  diphtheria.  They  may 
also  be  a  result  of  overeating  or  of  deranged  digestion. 
If  the  muscles  are  not  quickly  relaxed  by  placing  the 
child  in  a  warm  bath,  a  physician  should  be  called  with- 
out delay. 

514.  Poisons.  —  A  poison  is  any  substance  which  is  capa- 
ble, Avhen  taken  into  the  body,  of  producing  effects  in- 
jurious to  health  and  life.  Various  substances  in  common 
use  in  the  household  —  such  as  ammonia,  lye,  ratsbane, 
carbolic  acid  and  other  disinfectants  —  are  poisons.  Many 
medicines  (in  sufficient  quantities)  are  poisons,  and  all 
medicines  should  be  carefully  labeled  and  used  only  at 
such  times  and  in  such  quantities  as  are  prescribed  by  a 
physician. 


354  THE   PRESERVATION   OF   HEALTH 

515.    Poisons  are  usually  divided  into  two  classes  :  cor- 
rosive or  irritant  poisons,  and  narcotics. 

Corrosive  poisons  cause  great  changes  in  the  tissues. 
In  this  class  are  included  all  those  which  affect  the  skin, 
causing  inflammation  and  sometimes  destruction  of  the 
tissues ;  those  which  act  upon  the  mucous  membranes  of 
the  alimentary  canal,  giving  rise  to  inflammation,  nau- 
sea, vomiting,  pain,  and  purging  ;  and  those  which  act 
upon  the  mucous  lining  of  the  respiratory  organs.  These 
last  are  usually  gases.  A  poison  to  affect  the  system  must 
be  in  liquid  or  gaseous  form,  but  solid  poisons  may  be 
quickly  dissolved  by  the  fluids  of  the  mouth  or  the  stom- 
ach, or  the  exudations  from  the  broken  surface  of  the 
skin,  and  the  solution  becomes  dangerous.  Some  solid 
poisons,  however,  dissolve  so  slowly  that  they  may  pass 
through  the  alimentary  canal  and  be  expelled  from  the 
body  without  doing  harm.  Those  poisons  which  enter  the 
blood,  and  by  causing  alterations  in  it,  or  by  circulating 
in  the  blood,  injuriously  affect  various  organs,  belong  to 
the  class  of  irritants.  The  symptoms  resulting  differ  as 
one  organ  or  another  is  most  affected. 

516.  Narcotics  do  not  produce  marked  tissue  changes, 
but  affect  chiefly  the  nervous  system.  The  results  vary 
greatly.  Sometimes  convulsions,  cramps,  delirium  ;  some- 
times depression,  sleep,  or  stupor  may  be  caused.  Nar- 
cotics work  their  effects  more  slowly  than  do  the  irritants, 
and  the  particular  symptoms  which  appear  depend  so  much 
upon  the  special  susceptibility  of  the  individual  that  diag- 
nosis is  often  very  difficult.  Some  poisons  which  produce 
narcotic  effects  are  also  corrosive  to  the  tissues,  so  that  the 
classification  into  irritants  and  narcotics  is  not  an  absolute 
and  scientific  one. 

517.  Treatment.  —  In  case  of  poisoning,  the    object    of 


COMMON   ACCIDENTS   AND   INJURIES 


355 


treatment  is  to  prevent  absorption  of  the  dangerous 
substance  and  local  injury  to  the  tissues.  It  is  usually 
desirable  to  cause  vomiting.  This  may  often  be  done 
simply  by  thrusting  a  finger  into  the  throat  :  or  a  table- 
spoonfal  of  ground  mustard,  or  of  common  salt,  in  a  glass 
of  warm  water,  or  even  lukewarm  water  alone  may  act  as 
au  emetic.  Vomiting  should  be  induced  repeatedly,  and 
then  the  antidote  for  the  poison,  if  known,  shoidd  be  given; 
and,  if  the  poison  is  an  irritant,  slimy  fluids,  such  as  white 
of  egg,  mucilage,  flaxseed  tea.  or  barley  water,  shoidd  be 
swallowed  in  order  to  protect  the  walls  of  the  alimentary 
caual  from  its  action.  In  certain  cases,  however,  emetics 
shoidd  not  be  used. 

518.   Table  of  Common  Poisons  :  Symptoms  and  Antidotes.  — 


Acids 
Carbolic 
Hydrochloric 
Xitric 
Oxalic 

Sulphuric  (the  most 
serious) 


SYMPTOMS 


Blistering    and    burn- 
ing of  the  surface ;  I 
intense    inflamma-  l 

tiou  of  s  t  o  ni  a  c  h  .  | 
Carbolic  acid  causes  j 
nervous  symptoms  j 
also  —  great  weak-  \ 
uess. 


TKEATMENT 

Weak  alkalis,  magne- 
sia, common  soda, 
chalk,  soap,  dilute 
ammonia,  etc.,  after- 
ward mucilaginous 
drinks,  wliite  of  egg, 
milk,  etc.  For  ox- 
alic acid  give  lime ; 
other  alkahes  are  not 
antidotes  for  it. 

Treat  corroded  sur- 
faces   like    burns. 

Give  no  emetic. 


Alkalis 

Ammonia 

Caustic    potash,    or 

soda 
Lye 
Saltpeter 


Symptoms   similar  to 
those  caused  by  acid  < 
poisoning. 


f  Weak  acids  — vinegar, 
or  lemon  juice ;  olive 
oil,  melted  butter, 
ere  a  m  .  Give  no 
emetic.  Soothing 
applications  to  sur- 

l      faces. 


356 


THE   PRESERVATION   OF   HEALTH 


POISONS 


Arsenic 

Paris  green 

Rat  poison 

Mercury,  as  corro- 
sive sublimate 

Lead,  as  sugar  of 
lead,  or  white 
paint. 


SYMPTOMS 


Vomiting,  inflamma- 
tion of  stomach, 
cramps  in  abdomen, 
thirst;  sometimes 
abdominal  symp- 
toms almost  absent, 
and  delirium,  coma, 
convulsions,  lead  to 
speedy  death. 


TREATMENT 

Cause  repeated  vomit- 
ing (except  in  mer- 
cury poisoning). 
The  antidote  for  ar- 
senic is  oxide  of  iron; 
for  lead,  Epsom  salts. 
After  the  antidote 
for  arsenic,  give 
strong  solution  of 
common  salt ;  after 
Epsom  salts  give  oils, 
flour  and  vrater ;  for 
mercury,  give  vv^hite 
of  Q^g,  milk,  or  other 
albuminous  material. 


Phosphorus  from 
matches,  rat  poi- 
sons, phospho- 
rated oil. 


Severe  pain  in  stom- 
ach, eructation  and  Stomach  must  be  emp- 
tied thoroughly. 
Give  strong  soap- 
suds or  magnesia 
in  water.  Do  not 
give  oils. 


vomiting :  gases  and 
solids  having  phos- 
phorescent odor. 
Later,  unconscious- 
ness, collapse,  con- 
vulsions. 


Strychnine 


Intense  excitement  of 
spinal  cord  and  gen- 
eral nervous  system, 
causing  cramps,  con- 
vulsions, lockjaw, 
etc. 


Chloral,  opium,  and 
bromide  of  potash 
are  antidotes ;  empty 
the  stomach  as 
quickly  as  possible, 
then  give  antidote. 


Chloral 


Deep  sleep  without 
previous  excitement, 
passing  into  coma, 
death  resulting  from 
sudden  heart  failure. 


Stomach  must  be 
quickly  emptied  and 
strong  stimulants 
given  —  such  as 
strychnine,  atropine, 
etc. 


COMMON  ACCIDENTS   AND   INJURIES 


357 


POISONS 


Opium 
jMorph  ine 
Paregoric 
Laudanum 
Dover's  powder 
Soothing  sirups, 


etc. 


SYMPTOMS 

First,  state  of  mild, 
mental  excitement ; 
later,  drowsiness, 
sleep,  then  complete 
unconsciousness, 
while  pulse  grows 
weak  and  irregular, 
skin  cold  and  moist.  ^ 
Pupils  of  the  eyes 
grow  smaller  and 
smaller,  respiration 
becomes  very  slow, 
and  patient  dies 
from  failure  of 
breathing. 


TREATMENT 

Stomach  must  be  emp- 
tied and  repeatedly 
washed  out  w  i  t  h 
water.  Patient  must 
be  kept  awake  by 
constant  movement, 
dashes  of  cold  water, 
strong  coffee,  or  even 
strychnine.  The 
muscles  of  respira- 
tion may  be  stimu- 
lated by  electricity ; 
and  cases  where 
death  has  appar- 
ently occurred  may 
be  saved  by  forced 
artificial  respiration . 


Aconite 


General  n  umbness, 
weakness,  and  cold 
sweat ;  tingling  in 
throat. 


Cause  free  vomiting. 
Give  stimulating 
drinks  —  coffee,  etc. 


Belladonna 


Eyes    bright,    pupils 
dilated ;  mouth  and 
I       throat  dry.     Some- 
l-      times  convulsions. 


Empty  the  stomach 
thoroughly.  Give 
tannic  acid  or  strong 
bark  tea. 


Other  Vegetable 
Poisons 

Wild  parsley 

Bitter  sweet  berries 

Mountain    ash    ber- 
ries 

Indian  tobacco 

Toadstools 

Hemlock 

Tobacco,  etc. 


Nausea,  weakness,  stu- 
por, etc. 


Empty  the  stomach 
and  intestines ;  give 
stimulants. 


358 


THE   PRESERVATION   OF   HEALTH 


POISONS 

Putrefactive  Poisons 
Foods  which  have 
begun  t  o  decay 
sometimes  give 
rise  to  deadly  poi- 
sons. These  most 
often  appear  in 
meat,  sausage,  and 
cheese;  while  a 
particular  poison 
called  tyrotoxicon 
is  developed  in 
milk,  ice  cream, 
etc.,  which  have 
stood  long  in  ves- 
sels not  kept  per- 
fectly clean,  or 
in  rooms  where 
germs  of  decay 
exist  —  as  from 
decaying  wood. 


SYMPTOMS 


TREATMENT 


Animal  Poisons 
Snake  bites 


Symptoms  vary 
greatly.  There  is, 
usually,  pain  in  the 
digestive  organs; 
sometimes  vomiting 
and  purging,  fol- 
lowed by  weakness. 


Give  mild  emetic  — 
mustard  or  pow- 
dered alum  in  warm 
water  —  then  vine- 
gar and  water. 
Castor  oil  may  be 
given  to  empty  the 
intestines. 


Local  pain  and  swell- 
ing, followed  by 
great  weakness,  diz- 
ziness, blood  poison- 
ing; sometimes 
death. 


Apply  tight  ligature 
between  the  wound 
and  the  heart.  Open 
the  wound  and  wash 
with  solution  of 
permanganate  of 
potassium ;  or  t  h  e 
poison  may  be 
drawn  out  by  suck- 
ing with  the  mouth 
or  with  a  cupping 
glass.  In  severe 
cases  the  wound 
should  be  burned 
with  hot  iron  or 
caustic.  Give  stimu- 
lants to  support  the 
system. 


COMMON  ACCIDENTS    AND    INJURIES 


359 


POISON 


Insects''  Stings 
Wasps 
Hornets 
Bees 
Mosquitoes,  etc. 


SYMPTOM 


Swelling,  pain;  in  se- 
vere cases  followed 
by  weakness. 


TREATMENT 

Generally  little  treat- 
ment is  needed. 
Bathe  with  carbolic 
acid,  diluted  with 
water,  to  relieve 
smarting.  Some  in- 
sect stings  are  acid, 
some  alkaline.  If 
the  application  of 
am  monia  or  wet  soda 
does  not  relieve,  try 
vinegar  or  lemon 
juice. 


CHAPTER   XXVI 
PUBLIC  HYGIENE,    OR  GENERAL  SANITATION 

519.  Definition. — As  personal  hygiene  is  tlie  art  and  the 
science  of  preserving  the  individual  body  in  health,  so 
public  hygiene  is  the  art  and  science  of  promoting  the 
health  of  the  community.  A  healthy  man  is  one  whose 
body  is  sound  and  vigorous  in  all  its  parts,  so  that  all  the 
functions  of  the  system  are  performed  perfectly,  easily, 
and  without  discomfort;  no  one  of  all  the  organs  neglect- 
ing or  failing  to  do  the  work  assigned  it,  and  so  deranging 
or  poisoning  other  organs. 

A  healthy  village  or  city  is  one  in  which  most  of  the 
inhabitants  are  healthy,  and  especially  one  in  which  con- 
tagious and  infectious  diseases  do  not  pass  from  one  per- 
son to  another. 

We  have  learned  that  a  man,  in  order  to  maintain  his 
health,  must  have  pure  air,  pure  water,  and  wholesome 
food.  But  in  crowded  towns  and  cities  even  the  wealth- 
iest citizens  are  not  able  to  procure  these  simple  necessities 
for  themselves.  The  carelessness  of  some  obscure  and 
ignorant  person  may  poison  the  water  supplied  to  rich 
and  poor  alike  ;  germs  of  disease  from  the  .most  squalid 
part  of  a  city  may  be  borne  by  the  air,  by  the  gas  of  a 
sewer  pipe,  or  in  any  one  of  a  thousand  other  ways  to 
carry  death  to  a  palace  many  miles  away.  A  single  filthy 
dwelling  may  poison  a  whole  town.       It  is  not   enough 


Pl-BLIC    HYGIENE,    OR    GENERAL   SANITATION        361 

that  intelligent  persons  should  themselves  live  according 
to  sanitary  laws  ;  it  is  necessary  to  their  health  that  the 
ignorant  and  careless  should  also  be  obliged  to  do  so. 
This  cannot  be  brought  about  by  individual  influence  or 
authority.  Hence  it  has  come  to  pass  that  in  all  civilized 
communities  some  degree  of  control  is  exercised  by  the 
officers  of  the  government  over  the  personal  habits  and 
ways  of  life  of  private  persons.  Many  of  the  laws  given 
by  Closes  to  the  Hebrews  and  preserved  in  the  Scriptures 
relate  to  sanitary  matters  connected  with  daily  life,  and 
it  is  believed  that  obedience  to  those  laws  has  had  much 
to  do  with  the  fact  that  the  Jews,  throughout  their  his- 
tory, have  been  remarkably  free  from  great  epidemics  of 
disease.  Neglect  of  sanitary  precautions  is,  on  the  other 
hand,  understood  to  be  responsible  for  the  frightful 
*'  plagues ''  which  often  swept  over  the  earth  in  past 
ages,  destroying  many  thousands  of  lives.  They  arise 
even  yet  in  the  filthy  cities  of  Oriental  countries,  but  are 
now  far  less  destructive  and  more  easily  kept  within 
bounds. 

Our  knowledge  as  to  what  the  power  of  government 
can  do  to  promote  the  health  of  a  community  has  been 
increasing  rapidly  in  recent  years,  but  that  knowledge  is 
far  from  being  thoroughly  applied,  because  the  people  in 
general  are  not  yet  intelligent  enough  to  demand  it. 

520.  Knowledg^e  of  Sanitary  Laws  Essential  to  Good 
Citizenship.  —  In  a  free,  democratic  government,  such  as 
ours,  proper  attention  to  sanitary  matters  on  the  part  of 
public  officers  depends  upon  an  intelligent  and  active 
public  sentiment.  Since  the  people  are  the  government, 
it  is  the  duty  of  the  people  —  all  the  people  —  to  see  to  it 
that  their  servants,  the  officers  appointed  to  protect  them 
against  the  dangers  of  unsanitary  conditions  in  any  part 


362  THE   PRESERVATION   OF   HEALTH 

of  the  town  or  city,  shall  do  their  duty.  No  man  can 
be  a  really  good  citizen  who  is  ignorant  of  the  condi- 
tions which  threaten  the  general  health,  or  who  neglects 
to  use  his  influence  to  keep  the  health  officers  watch- 
ful and  active.  The  subject  of  sanitation  should  there- 
fore receive  attention  in  our  schools,  and  may  properly 
be  considered  briefly  in  connection  with  the  study  of 
physiology. 

521.  A  Healthy  Town  or  City  is  one  in  which  the  poorest 
inhabitants  have  pure  air  to  breathe,  pure  water  to  drink, 
wholesome,  unadulterated  food  to  eat,  and  opportunities 
for  cleanliness  in  person  and  dwelling.  These  conditions 
can  be  supplied  only  by  the  strong  arm  of  a  central  power 
supported  by  an  enlightened  public  opinion.  And  having 
provided  these  prime  necessities,  the  central  power  of 
government  should  require  all  citizens  to  make  use  of 
them.  A  man  should  not  be  permitted  to  use  the  foul 
water  from  a  filthy  well,  even  on  his  own  premises;  nor 
to  keep  his  own  dwelling  in  so  uncleanly  a  state  as  to 
endanger  the  health  of  his  own  family  and  that  of  his 
neighbors;  if  public  washing  conveniences  are  provided 
he  should  even,  if  necessary,  be  obliged  to  have  the  cloth- 
ing of  his  family  cleansed  and  his  own  body  bathed, 

522.  Cleanliness  the  One  Essential.  —  The  conditions  of 
general  physical  well-being  may  after  all  be  reduced  to 
one,  viz.  cleanliness^  taken  in  its  broadest,  fullest  sense. 
That  would  include  clean  air,  clean  water,  unadulterated 
food,  cleanliness  of  person  and  clothing,  and  adequate  ex- 
ercise by  which  purity  of  blood  is  promoted  and  removal 
of  the  poisonous  waste  of  the  body  is  secured. 

523.  Pure  Air.  —  A  man  can  live  for  a  considerable  time 
without  food  or  water,  and  he  may  within  certain  limits 
safely  select  what  he  will  eat  and  drink.     But  he  cannot 


PUBLIC    HYGIENE,    OR   GENERAL   SANITATION        363 

live  for  a  single  hour  without  air,  and  he  is  unable  to 
select  what  air  he  will  use,  for  he  must  breathe  that  which 
immediately  surrounds  him.  Several  things  are  needful 
that  the  air  of  a  dwelling  or  other  building  may  be  fit  to 
breathe. 

(1)  Drainage  of  the  Grround  on  ivJiicJi  a  House  stands.  — 
More  or  less  of  the  air  in  a  building  comes  from  the  ground 
beneath  and  around  it.  A  wet  soil  favors  the  multiplica- 
tion of  the  bacteria  always  present  in  the  ground,  and 
among  them  are  often  germs  of  specific  disease.  Water 
is  found  at  varying  distances  everywhere  beneath  the 
earth's  surface,  and,  in  order  that  a  spot' may  be  fit  for 
building  upon,  what  is  called  the  ground  water  should  be 
not  less  than  fifteen  feet  below  the  surface  (some  authori- 
ties say  thirty  feet),  and  the  level  should  not  greatly  vary 
from  time  to  time.  That  a  house  may  be  healthful,  the 
soil  beneath  it  must  be  thoroughly  drained  by  pipes  laid 
deep  enough  in  the  ground  ;  and  public  authorities  should 
have  power  to  see  that  this  is  done. 

(2)  Grround  Air  sTioidd  so  far  as  possible  he  excluded  from 
a  House.  — The  air  in  a  house  is  usually  warmer  than  that 
outside,  and  so  there  is  a  tendency  to  suck  up  the  air  in 
the  porous  ground  below.  Even  if  the  soil  is  dry,  there 
are  often  gases  from  decaying  vegetation  or  other  sources, 
which  are  more  or  less  injurious  to  life,  mixed  with  the 
earth.  These  should  be  excluded  from  the  house  by  cov- 
ering cellar  walls  and  floor  with  an  impervious  coating. 
Care  must  also  be  taken  that  nothing  is  left  to  decay  in 
the  cellar  or  any  other  part  of  a  building. 

(3)  Sunshine  is  necessary  to  Health  and  to  the  purity  of 
the  air  in  a  house.  No  room  is  fit  for  human  occupancy 
if  it  does  not  at  some  time  receive  the  direct  rays  of  the 
sun.     Many  dangerous  germs  are  killed  outright  by  direct 


364  THE   PRESERVATION   OF   HEALTH 

sunlight.     Those  persons  who  live  habitually  shut  out  from 
sunshine  never  have  strong,  buoyant  health. 

It  is  not  yet  common  for  public  authorities  to  interfere 
in  respect  to  this  matter.  In  our  cities  it  is  even  permitted 
to  one  citizen  to  cut  off  completely  from  his  neighbor's 
family  this  prime  necessity  to  well-being. 

524.  The  Air  in  Streets  and  Alleys  is  often  rendered  offen- 
sive and  dangerous  by  accumulations  of  filthy  refuse  from 
dwellings,  stables,  factories,  etc.  Neglect  of  prompt  and 
thorough  cleansing  of  all  such  passages  by  the  officials 
whose  duty  it  is,  should  never  be  tolerated  for  a  day,  and 
cleanliness  of  private  premises  should  also  be  legally 
enforced. 

525.  Pure  Food.  —  Governmental  inspection  of  the  vari- 
ous foods  offered  for  sale  is  now  recognized  as  an  impor- 
tant duty.  Diseased  meat,  adulterated  milk,  butter,  lard, 
cheese,  etc.,  are  supposed  to  be  excluded  from  the  markets, 
while  adulterated  sugars,  baking  powder,  spices,  etc.,  are 
doubtless  less  common  than  formerly.  But  occasionally  an 
outbreak  of  typhoid  fever  or  other  fatal  disease  is  traced 
to  the  carelessness  or  ignorance  or  cupidity  of  some  dealer 
in  dairy  products,  and  hundreds  of  poor  families  are  found 
to  be  suffering  in  health  from  the  adulterated  bread  or 
flour  or  other  necessary  sold  by  an  unscrupulous  dealer. 
The  inspection  of  foods  should  be  made  much  more  strict, 
and  should  be  enforced  in  the  smaller  communities  as  well 
as  in  the  large  cities. 

526.  Pure  Water.  —  Nothing  is  more  essential  to  the 
health  of  a  community  than  an  abundant  supply  of  whole- 
some water  for  drinking,  and  good  citizens  look  well  to  the 
source  of  their  drinking  water.  Water  from  small  streams, 
rivers,  or  lakes  is  seldom,  in  thickly  settled  parts  of  the 
world,  pure  enough  for  drinking  until  it  has  been  treated 


PUBLIC   HYGIENE,    OR    GENERAL   SANITATION        365 

by  some  of  the  various  inetliods  now  in  use  for  freeing  it 
from  the  unwholesome  matters  ahnost  always  present.  It  is 
true  that  running  streams  and  lakes  exposed  to  the  action 
of  sun  and  wind  are  purified  to  a  considerable  extent  by 
natural  influences,  and  where  they  do  not  receive  an 
excessive  amount  of  the  waste  of  towns  and  factories, 
may  usually  be  safely  used.  But  very  often  the  filth  of 
a  city  or  of  several  cities  is  poured  continually  into  the 
lake  or  river  which  supplies  the  inhabitants  with  drinking 
water,  the  amount  of  poison  being  far  more  than  nature  is 
able  to  destroy.  In  such  cases  many  and  complicated 
devices  are  used  for  getting  rid  of  the  injurious  sub- 
stances. The  water  may  be  drawn  off  into  large  reser- 
voirs and  allowed  to  settle.  Then,  the  coarser  filth  having 
been  deposited,  the  water  may  be  drawn  into  other  reser- 
voirs and  treated  with  certain  chemicals  which  will  cause 
the  precipitation  of  other  substances  as  sediment.  Some 
chemical  substances  destroy  organic  matter  by  oxidizing 
it,  and  sometimes  the  same  result  is  obtained  by  forcing 
air  through  the  contaminated  water. 

Water  is  also  partly  purified  by  filtering  through  vari- 
ous porous  materials  —  large  beds  of  sand,  gravel,  and 
broken  stone,  for  instance.  The  filtering  body  itself  soon 
becomes  clogged  with  filth,  and  must  be  often  renewed 
or  cleansed. 

None  of  these  processes  destroys  all  the  dangerous  germs 
to  be  found  in  impure  w^ater,  and  it  is  a  wise  precaution 
for  every  family  to  boil  for  half  an  hour  all  water  for 
drinking  which  comes  from  a  source  liable  to  contamina- 
tion. The  water  may  then  be  placed  in  glass  cans,  tightly 
closed,  and  cooled  in  a  refrigerator,  or  in  a  cellar.  By 
this  course  much  illness  and  death  in  large  towns,  where 
typhoid  fever  and  other  water-borne  diseases  are  always 

macy's  phys. — 23 


366  THE   PEESERVATION   OF   HEALTH 

present,  would  be  prevented.  The  same  care  should  be 
taken  in  the  country,  when  the  drinking  water  comes 
from  springs  or  shallow  wells. 

Probably  the  safest  source  of  a  water  supply  is  from 
deep  wells,  sunk  far  below  any  possible  befoulment  from 
the  surface.  Many  towns  are  now  thus  supplied.  Ordi- 
nary wells  and  cisterns  are  seldom  safe,  unless  great  care 
is  used.  The  leakage  from  a  barnyard  or  cesspool  many 
rods  away  may  find  its  way  into  a  well  through  the  layers 
of  earth,  and  poison  the  water.  Rain  water  is  mixed  with 
dust  from  the  air  and  the  roof,  with  bits  of  leaves  and 
other  organic  matter,  and  should  be  thoroughly  filtered 
and  boiled  for  drinking. 

Ice  (unless  manufactured  from  distilled  water)  contains 
impurities,  and  should  not  be  put  into  water  used  for 
drinking. 

527.  Public  Bathing  and  Washing  Conveniences  are  now 
provided  by  the  most  progressive  cities,  and  contribute 
much  to  the  health  of  the  people.  They  should  be  free, 
or  so  nearly  so  that  the  poorest  families  may  be  able  to 
enjoy  the  luxury  of  cleanliness. 

528.  Disposal  of  Garbage  and  Sewage.  —  Not  only  must 
the  daily  waste  in  towns  and  cities  be  gathered  up  and 
removed  from  sight,  but  it  must  also  be  treated  in  some 
way  which  shall  destroy  its  dangerous  character.  It  must 
not  be  dumped  upon  vacant  lots  in  the  poorer  quarters  of 
the  town,  and  left  to  decay  and  poison  the  air.  And  it 
is  seldom  safe  to  pour  it  into  neighboring  water  ways  or 
lakes.  Various  devices  have  been  tried  for  the  better 
disposal  of  the  poisonous  waste  of  human  life,  no  one  of 
which  is  absolutely  best  for  all  localities.  That  which  is 
most  desirable  for  a  particular  community  must  be  deter- 
mined in  view  of   all   circumstances   and   surroundings. 


PUBLIC   HYGIENE,    OR    GENERAL   SANITATION        367' 

No  cheap  and  safe  method  has  yet  been  discovered.  All 
are  expensive,  but  any  one  is  cheaper  than  the  sacrifice  of 
life  and  health  which  is  sure  to  result  from  unsanitary  or 
slipshod  ways  of  dealing  with  this  serious  problem.  Some 
of  the  most  satisfactory  methods  in  use  in  the  most  pro- 
gressive cities  may  be  simply  mentioned  here. 

Where  a  very  large  body  of  water  is  at  hand,  which 
is  not  the  source  of  the  town's  water  supply,  the  sewage 
may,  for  a  time  at  least,  be  safely  poured  into  it.  This  is 
the  cheapest  way.  But  such  pollution  of  streams  and 
lakes  is  now  forbidden  by  law  in  many  countries  of 
Europe,  as  it  should  be  in  the  United  States.  In  some 
cities  the  sewage  is  collected  in  great  vats,  where  the  solid 
portion  is  separated  from  the  liquid,  and  sold  for  use  as 
a  fertilizer.  The  liquid  is  by  chemical  treatment  freed 
from  its  harmful  ingredients,  and  poured  into  the  water- 
courses. Some  cities  own  large  farms,  to  which  the  sewage 
is  conveyed  in  close  tanks,  and  spread  upon  the  soil  as  a 
fertilizer.  In  other  cases  the  soil  is  simply  used  as  a 
filter.  The  sewage  is  spread  upon  it,  and  the  liquid 
which  filters  through  is  received  by  drain  tiles  laid  below 
the  surface,  and  carried  into  a  natural  stream.  The  solid 
portion  is  decomposed  by  the  action  of  air,  sun,  and  bac- 
teria, which  render  it  harmless. 

Garbage  and  the  solid  portion  of  sewage  are  frequently 
consumed  in  great  furnaces,  that  which  remains  inde- 
structible by  fire  being  safely  used  for  filling  up  low 
places  about  the  city. 


GLOSSARY 

Ab-do'men  (Lat.)  :  the  cavity  of  the  body  lying  below  the  diaphragm 
and  containing  most  of  the  digestive  organs. 

Ab-du'cens  (Lat.,  leading  away):  the  sixth  pair  of  cranial  nerves. 

Ab-sorb'ents  (Lat.  absorbere,  to  suck  in)  :  the  vessels  which  take  up 
nutriment  or  waste  matter. 

Ab-sorp'tion  :  the  process  of  taking  up  food  from  the  alimentary  canal 
or  other  substances  from  the  tissues. 

Ac-cel'er-a-tor  (Lat.  accelerare,  to  hasten)  :  that  which  quickens,  as  an 
accelerator  nerve. 

Ac-com-mo-da'tion  of  the  eye  (Lat.  accommodare,  to  fit)  :  the  adjust- 
ment of  the  shape  of  the  crystalline  lens  for  distinct  vision  at  dif- 
ferent distances. 

Ac'id  (Lat.  acidus,  sour)  :  one  of  a  class  of  chemical  compounds  usu- 
ally sour  to  the  taste,  always  soluble  in  water,  capable  of  turning- 
vegetable  blue  to  red  and  of  destroying  the  distinctive  properties 
of  alkalis  or  bases.  Acids  combine  with  bases  to  form  salts,  and 
then  lose  their  own  distinctive  properties. 

Ac-tin'ic  energy  (Gr.  aktis,  aktinos,  ray)  :  that  form  of  force  in  light 
which  produces  chemical  changes. 

Ad'i-pose  (Lat.  adej)s,  fat)  :  that  form  of  tissue  which  forms  or  con- 
tains fat. 

Af fer-ent  (Lat.  ajferre,  from  ad,  to,  and  ferre,  to  bear)  :  conducting 
inward  or  toward  a  center;  opposed  to  efferent. 

Al-bu'men  (Lat.  albus,  white):  white  of  egg. 

Al-bu'min  (Lat.  albus,  white)  :  a  substance  composed  of  carbon,  ni- 
trogen, hydrogen,  and  oxygen,  found  in  animals  and  plants,  and 
an  essential  part  of  every  living  cell.  It  is  found  in  its  purest 
natural  form  in  the  white  of  an  egg. 

Al-bu'mi-noid  :  one  of  the  foods  containing  nitrogen  ;  a  proteid. 

Al'co-hol  (Arabic  al-kohl,  fine  powder  of  antimony,  used  in  the  East 
to  paint  the  eyebrows  with)  :  the  spirituous  or  intoxicating  ele- 
ment of  fermented  or  distilled  liquors  ;  or,  in  popular  speech,  any 
liquid  containing  it  in  a  considerable  quantity. 

369 


370  GLOSSAKY 

Al-i-men'ta-ry  (Lat.  alimentum,  food)  :  pertaining  to  food  or  concerned 
with  nutrition. 

Alimentary  canal :  the  passage  for  the  food,  in  which  digestion  takes 
place. 

Al'ka-li  (Arabic  al-kcdi,  al-qaliy,  ashes  of  the  plant  saltwort)  :  one  of 
a  groujD  of  caustic  bases  (such  as  soda  and  potash)  which  are  solu- 
ble in  water,  have  the  power  of  neutralizing  acids  and  forming 
salts  with  them,  of  uniting  with  fats  to  form  soaps,  and  of  chan- 
ging the  tint  of  many  vegetable  colorings  —  as  of  litmus  reddened 
by  acid  —  to  blue. 

Al-ve'o-lus  (Lat.,  a  small  cavity)  :  a  small  sac  or  vesicle ;  one  of  the 
air  cells  of  the  lungs. 

A-mce'ba  (Gr.  amoibe,  change,  exchange)  :  one  of  the  lowest  forms  of 
animal  life,  consisting  of  a  single  cell  which  is  capable  of  many 
changes  of  form. 

Am-pulla  (Lat.,  a  narrow-necked  vessel  having  two  handles  and 
swelling  out  below)  :  one  of  the  dilations  of  the  semicircular  canals 
of  the  ear. 

A-nab'o-lism  (Gr.  anabole,  something  heaped  up)  :  the  constructive 
processes  of  the  body ;  opposed  to  kataholism. 

A-nat'o-my  (Gr.  anatome,  dissection,  from  anatemnein,  to  cut  up)  : 
the  science  which  treats  of  the  structure  of  organic  bodies. 

An-te'ri-or :  toward  the  head,  or  toward  the  front  of  the  body. 

An'ti-dote  (Gr.  anti,  against,  and  didonai,  to  give)  :  a  substance  that 
prevents  a  poison  from  injuring  the  tissues,  when  taken  into  the 
body. 

An-ti-sep'tic  (Gr.  anti,  against,  and  septikos,  septic,  making  putrid)  : 
having  the  power  to  prevent  putrefaction. 

An-ti-tox'in  (Gr.  anti,  against,  and  toxikon,  poison)  :  a  substance  which 
neutralizes  the  action  of  a  toxin,  or  animal  poison. 

A'nus  (Lat.)  :  the  opening  at  the  lower  end  of  the  alimentary  canal, 
through  which  the  excrements  are  discharged. 

A-or'ta  (Gr.  aorte,  from  aeirein,  to  raise,  to  lift)  :  the  great  artery  ris- 
ing from  the  left  ventricle  of  the  heart. 

Ap-pen-dic'u-lar  skeleton :  the  pectoral  girdle,  the  pelvic  girdle,  and  the 
bones  of  the  limbs. 

Ap-pen'dix;  plural  Ap-pen'di-ces  (Lat.,  from  appendere,  to  hang)  :  an 
appendage.  The  vermiform  appendix  is  a  small  portion  of  the 
intestine,  appended  to  the  c?ecum.  The  term  appendices  is  given 
to  the  earlike  projections  from  the  auricles  of  the  heart. 


GLOSSARY  371 

Aq'ue-duct  of  Syl'vi-us :  a  channel  connecting  the  third  and  fourth 

ventricles  of  the  brain.     Named  from  the  famous  anatomist  Dubois 

or  Sylvius  (the  latinized  form  of  the  name). 
A'que-ous  hu'mor:  the  fluid  filling  the  anterior  chamber  of  the  eyeball. 
A-rach'noid  (Gr.  arachnoeides,  like  a  cobweb)  :  the  middle  one  of  the 

three  membranes  of  the  brain  and  spinal  cord. 
A-re'o-lar  tissue  (Lat.  areola,  diminutive  of  area,  a  broad  space  of 

level  ground)  :    a  fibrous   connective   tissue  with   loosely  woven 

fibers  and  many  spaces. 
Ar'gon  (Gr.  argos,  lazy,  inert) :  a  gas  forming  about  one  per  cent  of 

the  atmosphere  ;  first  recognized  in  1895. 
Ar'ter-y  (Gr.  or  Lat.  arteria,  windpipe) :  one  of  the  tubes  conveying 

blood  from  the  heart.     They  were  formerly  thought  to  contain  air 

and  to  be  branches  of  the  windpipe. 
Ar-tic-u-la'tion  (Lat.  articidatus,  furnished  with  joints) :  any  junc- 
tion between  bones  in  the  skeleton. 
A-ryt'e-noid  cartilages  (Gr.  arutainoekles,  shaped  like  a  ladle,  from 

arutaina,   ladle,   and   eidos,   form) :    two   small  cartilages    of   the 

larynx. 
As-phyx'i-a  (Gr.  a-,  without,  and  sphuzein,  to  throb,  beat)  :  apparent 

death  from  stoppage  of  respiration,  as  in  suffocation  from  drowning 

or  the  breathing  of  certain  gases. 
As-sim-i-la'tion  (Lat.  assimUatio,  from  assimilare,  to  make  like)  :  the 

final  process  of  anabolism,  by  which  nutritive  material  is  converted 

into  the  living  substance  of  the  body. 
A-stig'ma-tism  (Gr.  a-,  without,  and  stigma,  stigmatos,   prick   of   a 

pointed  instrument,  spot)  :   a  defect  of  the  eye  due  to  irregular 

curvature  of  the  refractive  media,  by  reason  of  which  rays  of  light 

from  a  point  are  not  brought  to  a  single  focal  point.     It  results 

in  indistinctness  of  vision. 
At'las  (Gr.,  one  of  the  gods  who  bears  up  the  pillars  of  heaven)  :  the 

first  vertebra  of  the  neck,  supporting  the  weight  of  the  head. 
At'om  (Gr.  a-,  without,  and  tomos,  cut)  :  one  of  the  ultimate  indivisible 

particles  of  matter. 
Au'di-to-ry  os'si-cles  :  the  three  small  bones  of  the  middle  ear. 
Au'ri-cle  (Lat.  auricula,  diminutive  of  auris,  ear)  :  a  cavity  at  the  base 

(upper  portion)  of  the  heart. 
Au-to-in-tox-i-ca'tion  (Gr.  auto,  self,  and  Eng.  intoxication,  poisoning)  : 

a  poisoning  of  the  system  from   the  products   of  physiological 

processes  or  from  the  reabsorption  of  waste  matter. 


372  GLOSSARY 

Ax'i-al  skeleton :  the  bones  of  the  head,  neck,  and  trunk. 
Ax'il-la-ry  (Lat.  axilla,  the  armpit)  :   belonging  to  the  armpit,  as  the 

axillary  arteries. 
Ax'is  (Lat.,  axle)  :  the  second  vertebra  of  the  neck. 
Ax'is  cyl'in-der  :  the  central  core  of  a  nerve  fiber. 

Ba-cil'li  (plu.  of  mod.  Lat.  bacillus,  diminutive  of  baculum,  stick)  : 
microscopic,  rod-shaped  vegetable  organisms;  a  variety  of  bac- 
terium. 

Bac-te'ri-a  (plu.  of  bacterium,  from  Gr.  baklerion,  a  staff)  :  microscopic 
vegetable  organisms,  usually  in  the  form  of  jointed  rodlike  threads. 
They  are  found  in  connection  with  putrefying  matter.  Some  sorts 
cause  disease. 

Bi'ceps  (Lat.,  having  two  heads,  from  bis,  twice,  and  caput,  head)  : 
the  muscle  on  the  inner  side  of  the  upper  arm. 

Bi-cus'pid  valves  (Lat.  bi,  two,  and  cuspis,  a  point)  :  the  valves  guard- 
ing the  opening  from  the  left  auricle  of  the  heart  into  the  left 
ventricle ;  the  mitral  valves. 

Bicuspids :  the  two  double-pointed  teeth  on  each  side  of  each  jaw. 

Bile  (Lat.  bills)  :  a  greenish  yellow  fluid  secreted  ^by  the  liver.  It 
passes  into  the  small  intestine,  where  it  assists  in  the  digestion  of 
the  food. 

Bi-ol'o-gy  (Gr.  bios,  life,  and  locjia,  discourse)  :  the  science  of  life. 

Blind  spot :  an  elevated  surface  on  the  retina  where  the  optic  nerve 
fibers  enter  the  eye. 

Brach'i-al  (Lat.  brachium,  arm):  pertaining  to  the  arm,  —  as  the 
brachial  artery. 

Bron'chi  (Gr.  brogchos,  windpipe)  :  the  subdivisions  of  the  trachea. 

Cae'cum  (Lat.  ccecus,  blind)  :  the  first  division  of  the  large  intestine. 
Cal'ci-um  (Lat.  calx,  calcis,  lime)  :  a  chemical  element  found  in  lime, 

gypsum,  and  other  substances. 
Ca-nines'   (Lat.   canis,  dog)  :    the  sharp,  pointed    teeth   next   to  the 

incisors. 
Cap'il-la-ry  (Lat.  capillus,  hair)  :  one  of  the  smallest  blood  vessels  or 

other  minute  tubes. 
Car-bo-hy'drates  {carbon  and  hydrate)  :  a  class  of  foods  which  includes 

starch,  the  sugars,  and  cellulose.     They  are  composed  of  carbon, 

oxygen,  and  hydrogen. 
Car'bon  (Lat.  carbo,  coal)  :  a  chemical  element  found  in  all  organic 

compounds.     Diamond  and  graphite  are  forms  of  carbon. 


GLOSSARY  373 

Carbon  di-ox'ide:    a  gas   composed   of  oxygen   and  carbon,  always 

present  in  expired  air;  also  called  carhonic  acid  gas. 
Car'bon-ate:  a  salt  of  carbonic  acid,  as  limestone. 
Car'di-ac  (Gr.  kardia,  the   heart)  :   pertaining  to   the   heart,  as   the 

cardiac  nerves. 
Ca-rot'id  arteries  (Gr.  karotides,  from  karos,  heavy  sleep.     The  early 

Greeks  believed  these  arteries  in  some  way  caused  drowsiness)  : 

one  of  the  two  main  arteries  of  the  neck  carrying  blood  from  the 

aorta  to  the  head. 
Car'pus  (Gr.  karjjos)  :  the  wrist. 

Car'ti-lage  (Lat.  cart'dago) :  a  translucent  elastic  tissue;  gristle. 
Cartilages  of  San-to-ri'ni :  little  horn-shaped  projections  on  top  of  the 

arytenoids  in  the  larynx. 
Cartilages  of  Weis'berg:    small   bits   of  cartilage  in   folds   of   the 

mucous  membrane  of  the  larynx. 
Cell :  one  of  the  ultimate  units  of  which  all  living  bodies  are  com- 
posed. 
Cel'lu-lose :  the  substance  which  constitutes  the  essential  part  of  the 

solid  framework  of  plants.     It  is  a  carbohydrate. 
Cen'trum  (Lat.,  center)  :  the  stout,  bony  body  of  a  vertebra,  to  which 

is  attached  the  neural  arch. 
Cer-e-bel'lum  (Lat.,  diminutive  of  cerebrum,  brain)  :  the  large  lobe  of 

the  hind  brain  between  the  cerebrum  and  the  medulla  oblongata. 
Cer'e-bro-spi'nal  fluid :  the  watery  substance  which  fills  the  cavities 

of  the  brain  and  the  spinal  canal,  and  bathes  the  outer  surfaces  of 

the  brain  and  spinal  cord. 
Cerebro-spinal  me-nin'ges    (Gr.   menigx,   a   membrane) :    the  three 

membranes  of  the  brain  and  spinal  cord. 
Cerebro-spinal  men-in-gi'tis :  inflammation  of  the  membranes  of  the 

brain  and  spinal  cord. 
Cerebro-spinal  system:  the  brain  and  spinal  cord,  with  the  nerves 

arising  from  them. 
Cer'e-brum    (Lat.,  brain)  :   the   anterior   and  principal   part   of   the 

brain. 
Cer'vi-cal  (Lat.  cervix,  neck)  :    of   or  belonging  to  the  neck,  as  the 

cervical  vertebrae. 
Chem'i-cal  a-nal'y-sis :   the  separation  of  a  compound  substance,  by 

chemical  processes,  into  its  constituent  elements. 
Chemical  element :  a  substance  which  cannot  be  decomposed  by  any 

known  means  into  two  or  more  kinds  of  matter. 


374  GLOSSARY 

Chlo'ride :  a  compound  of  the  element  chlorine  with  some  other  ele- 
ment, as  chloride  of  sodium  (common  salt). 
Cho'roid :   the  second  of  the   coats  of  the  eye.     It  contains  a  dark 

pigment. 
Chyle  (Gr.  chulos,  juice)  :  a  milky  fluid  containing  partly  digested  food, 

and  especially  the  fatty  matter  of  the  food  in  a  state  of  emulsion. 
Chyme  (Gr.  chumos,  juice)  :  the  partly  digested  food  as  it  passes  from 

the  stomach  into  the  small  intestine. 
Cil'i-a  (Lat.  cilium,  eyelid)  :  small  hairlike  appendages  lining  certain 

organs,  as  the  air  passages. 
Cil'ia-ry  muscles :   small  muscles  which  help  to  adjust  the  eye  for 

seeing  at  different  distances. 
Ciliary  processes :   radiating  folds  of  the  choroid  of  the  eye  at  the 

outer  edge  of  the  iris. 
Cir-cum-val'late  pa-pil'lae  (Lat.  circum,  around,  and  vallum,  wall)  : 

a  form  of  papillae  found  at  the  back  of  the  tongue  and  containing 

some  of  the  taste  end  organs. 
Clav'i-cle  (Lat.  claoicula,  a  little  key)  :  the  collar  bone. 
Co-ag-u-la'tion  (Lat.  coagulatio)  :  the  change  of  a  liquid  to  a  thickened, 

curdlike  state  because  of  some  chemical  change. 
Coc'cyx  (Gr.  kokkux,  cuckoo)  :  the  end  of   the  vertebral  column  be- 
yond the  sacrum. 
Cochle-a  (Lat.,  a  snail)  :  a  spiral  bony  tube  of  the  internal  ear. 
Coe'li-ac  axis  (Gr.  koilos,  hollow,  and  Lat.  axis,  axle,  pole)  :  a  short, 

thick   branch   of  the  abdominal  aorta  given   off  just  below  the 

diaphragm. 
Colon  (Lat.  and  Gr.)  :  the  middle  and  longest  division  of  the  large 

intestine. 
Color  blindness  :  inability  to  distinguish  colors. 

Co'ma  (Gr.,  lethargy)  :  deep  stupor  from  which  it  is  diflBcult  or  im- 
possible to  rouse  a  person. 
Con-duc-tiv'i-ty  (Lat.  conducere,  to  bring  together)  :  the  power  of 

passing  on  a  stimulus  from  one  point  to  others. 
Con-ges'tion  (Lat".  con,  together,  and  gerere,  to  bring)  :  overfuUness 

of  the  blood  vessels  of  a  part  of  the  body. 
Con-junc-ti'va  (Lat.  conjunctivus,  connective)  :  the  mucous  membrane 

covering  the  external   surface   of  the   eyeball  and  forming  the 

lining  of  the  lids. 
Con-nect'ive  tissues :  tissues  devoted  to  the  support  and  connection 

of  the  muscles  and  nerves. 


GLOSSARY  375 

Con'scious-ness  (Lat.  con,  together,  and  scire,  to  know)  :  knowledge 

of  one's  own  mental  operations. 
Con-tract'ile  substance  (Lat.  contrahere,  to  draw  together)  :  the  soft, 

half-fluid  material  of  light  and  dark  disks  composing  the  muscle 

cells  of  voluntary  muscles. 
Con-trac-til'i-ty  :   the  power   possessed   by  living  cells  of  changing 

form  independently  of  pressure. 
Co-or-di-na'tion  (Lat.  co,  together,  and  ordinare,  arrange)  :  the  act  of 

arranging  in  due  order  or  relation. 
Co'ri-um  (Lat.,  a  hide,  leather)  :  the  innermost  layer  of  the  skin ;  the 

true  skin. 
Cor'ne-a  (Lat.  corneus,  horny)  :  the  transparent  part   of  the  coat  of 

the  eye  which  covers  the  iris  and  pupil. 
Cor'o-na-ry  arteries  (Lat.  corona,  crown)  :  the  arteries  of  the  heart 

itself. 
Coronary  veins  :  the  veins  of  the  wall  of  the  heart. 
Cor'po-ra  quad-ri-gem'i-na   (Lat.,  fourfold  bodies)  :  one  of  the  five 

chief  divisions  of  the  brain ;  called  also  the  optic  lobes. 
Cor'pus-cle  (Lat.  corpusculum,  diminutive  of  corpus,  a  body)  :  a  minute 

particle  or  cell,  as  a  blood  corpuscle,  a  lymph  corpuscle. 
Cor'pus  cal-lo'sum  (Lat.,  callous  body)  :  the  great  white  band  of  nerve 

tissue  connecting  the  hemispheres  of  the  cerebrum. 
Cor-re-late'    (Lat.  con,   together,   and  relatus,   referred)  :  to  place   in 

mutual  or  reciprocal  relations  ;  to  establish  a  relation  of   inter- 
dependence. 
Cor'tex  (Lat.,  bark)  :  an  outer  layer,  as  of  the  brain  or  the  kidney. 

The  cortex  of  the  brain  consists  mostly  of  gray  matter. 
Cos'tal    (Lat.    costa,   rib) :    pertaining   to   the   ribs   or   side   of    the 

body. 
Cra'ni-al :  belonging  in  any  way  to  the  cranium,  as  the  cranial  nerves 

or  arteries. 
Cra'ni-um  (Lat.,  from  Gr.  kranion,  the  skull)  :  the  human  skull. 
Cri'coid  (Gr.  krikos,  ring,  and  eidos,  form)  :  a  circular  cartilage  of  the 

larynx. 
Cni'ra  cer'e-bri  (Lat.,  literally,  the  legs  of  the  brain)  :  the  bands  of 

nervous  matter  connecting  the  cerebrum  with  the  medulla. 
Crys'tal-line  lens :  the  principal  lens  of  the  eye,  lying  just  back  of 

the  pupil. 
Cu'ti-cle  (Lat.  cuticida,  from  cutis,  the  skin)  :  the  epidermis  or  outer- 
most layer  of  the  skin. 


376  GLOSSARY 

De-cus-sa'tion  of  the  pyramids  (Lat.  decusmtio,  crossing)  :  the  cross- 
ing of  the  bundles  of  white  nerve  fibers  called  the  pyramids,  in  the 
medulla  oblongata. 

De-lir'i-um  tre'mens  (Lat.  delirium,  madness,  and  tremens,  trembling)  : 
a  disorder  of  the  brain  due  to  the  excessive  use  of  ardent  spirits. 

Den' tine  (Lat.  dens,  dentis,  tooth) :  the  principal  solid  tissue  of  the 
teeth. 

Der'mis  (Gr.  derma,  the  skin)  :  the  corium,  or  true  skin. 

Di'a-phragm  (Gr.  diaphragma,  a  partition  wall)  :  the  membranous  and 
muscular  division  between  the  thorax  and  the  abdomen. 

Dif-fer-en-ti-a'tion  of  tissues  (Lat.  differentia,  difference)  :  that  modi- 
fication in  the  structure  of  the  tissues  which  adapts  them  to  dif- 
ferent functions. 

Dif-fu'sion  of  gases :  the  homogeneous  mixture  which  takes  place  in 
two  gases  placed  in  contact. 

Di-ges'tion  (Lat.  digestio)  :  conversion  of  food  in  the  alimentary  canal 
into  products  which  can  be  absorbed  into  the  blood. 

Dor'sal  (Lat.  dorsum,  the  back)  :  of  or  pertaining  to  the  back,  as 
dorsal  m  uscles  ;  opposed  to  ventral. 

Duct :  a  tube  or  canal ;  especially  one  conveying  secretion  from  a 
gland. 

Du-o-de'num  (Lat.  duodeni,  twelve  each :  because  the  length  of  the 
duodenum  is  about  twelve  fingers'  breadth)  :  the  first  division  of 
the  small  intestine,  next  the  stomach. 

Du'ira  ma'ter  (Lat.,  hard  mother.  The  membrane  was  once  thought 
to  give  rise  to  every  membrane  of  the  body)  :  the  tough,  fibrous 
membrane  surrounding  the  brain  and  spinal  cord  and  lining  the 
cavities  of  the  skull  and  spinal  column. 

Em'bry-o  (Gr.  emhruon)  :  the  early  form  of  an  animal  in  develop- 
ment. 

E-mul'sion  (Lat.  emulgere,  emulsum,  to  milk  out) :  a  mixture  of 
liquids  which  do  not  dissolve,  the  particles  of  one  floating  as  small 
globules  in  the  other;  as  fat  (butter)  in  milk. 

En-am'el :  the  hard  outer  part  of  the  tooth. 

End  bulbs  :  one  form  of  touch  end  organs. 

End  organs  :  special  nerve  cells  or  groups  of  nerve  cells  which  receive 
and  pass  on  the  stimulus  to  which  they  are  adapted. 

End  plate :  the  branching  termination  of  a  nerve  fiber  in  a  muscle 
cell. 


GLOSSARY  377 

En-do-car'di-um  (Gr.  endon,  within,  and  kardia,  the  heart)  :  the  mem- 
brane lining  the  cavities  of  the  heart. 

En-do-skel'e-ton  (Gr.  endon,  within,  and  Eng.  skeleton)  :  the  inner 
bony  framework  possessed  by  vertebrate  animals. 

En-do-the'li-um  (Gr.  endon,  within,  and  thele,  nipple)  :  the  thin  epi- 
thelium lining  blood  vessels,  lymphatics,  and  serous  cavities. 

Ep-i-der'mis  (Gr.,  epi,  upon,  and  derma,  skin)  :  the  outer  layer  of  the 
skin,  which  is  without  blood  vessels  and  nerves,  and  without  sensa- 
tion. 

Ep-i-glot'tis  (Gr.,  from  epi,  upon,  and  glotta,  tongue)  :  a  lidlike  sheet 
of  cartilage  which  closes  the  glottis  while  food  or  drink  passes 
into  the  pharynx. 

Ep-i-theli-um  (Gr.  epi,  upon,  and  thele,  nipple)  :  the  superficial  layer 
of  cells  of  the  skin  and  mucous  membrane,  and  of  the  blood  vessels, 
lymphatics,  etc. 

E-soph'a-gus  (Gr.  oisophagos,  the  gullet)  :  that  part  of  the  alimentary 
canal  between  the  pharynx  and  the  stomach. 

E'ther  (Gr.  aiiJier,  from  aithein,  to  burn,  blaze)  :  a  thin,  elastic  medium 
supposed  to  pervade  all  space. 

Eth'moid  (Gr.  ethmoeldes,  like  a  sieve)  :  the  bone  through  which  the 
olfactory  nerves  pass  out  of  the  cranium. 

Eu-sta'chi-an  tube  (named  from  Eustachi,  an  Italian  physician)  :  the 
small  tube  connecting  the  tympanum  and  the  pharynx. 

Ex-cre'tion  (Lat.  excemere,  excretum,  to  sift  out)  :  the  act  of  discharg- 
ing from  the  body  useless  or  worn-out  material. 

Ex-0-skere-ton  (Gr.  exo,  without,  and  Eng.  skeleton)  :  the  outer  hard 
crust  or  covering  of  many  of  the  invertebrate  animals. 

Ex-pi-ra'tion  (Lat.  ex,  out,  and  spirare,  to  breathe)  :  the  act  of  breath- 
ing out;  opposed  to  inspiration. 

Fau'ces  (Lat.,  throat)  :  the  narrow  passage  from  the  mouth  to  the 
pharynx. 

Fe'mur  (Lat.,  thigh)  :  the  thigh  bone. 

Fe-nes'tra  (Lat.)  :  a  window.  The  fenest7Yi  oralis  andfetiestra  rotunda 
are  the  oval  and  round  openings  in  the  bone  between  the  cavity  of 
the  tympanum  and  the  labyrinth  of  the  ear. 

Fer'ment  (Lat.  fermentum,  tumult,  agitation)  :  that  which  causes  fer- 
mentation, as  yeast. 

Fer-men-ta'tion  :  the  transformation  of  an  organic  substance  into  new 
chemical  compounds  by  the  action  of  a  ferment. 


378  GLOSSARY 

Fi'brin  (Lat.^ftra,  thread)  :  a  white  fibrous  substance  formed  in  the 

clotting  of  the  blood. 
Fi-brin' o-gen  :  a  substance  in  the  blood  which  forms  or  helps  to  form 

fibrin,  and  thus  causes  clotting. 
Fib'u-la  (Lat.,  clasp,  buckle)  :  the  outer  and  smaller  of  the  two  bones 

of  the  leg. 
Firi-f orm  pa-pil'lae :  one  form  of  the  papillae  of  the  tongue,  containing 

end  organs  for  taste. 
Fissure  of  Ro-lan'do :  the  furrow  separating  the  frontal  from  the  pari- 
etal lobe  in  the  brain. 
Floating  ribs :  the  two  lowest  pairs  of  ribs,  in  man.     They  are  not 

connected  with  the  others  in  front. 
Food:  that  which,  taken  into  the  alimentary  canal,  supplies  material 

for  the  growth  and  repair  of  tissue,  for  the  generation  of  force,  or 

for  the  regulation  of  force. 
Food  elements :  the  five  classes  of  food  substances  necessary  to  the 

health  of  the  body,  viz.  proteids,  carbohydrates,  fats,  water,  salts. 
Fo-ra'men  mag'num  (Lat.  irom.  forare,  to  bore,  pierce ;  magnus,  great) : 

a  large  opening  in  the  occipital  bone  of  the  skull,  through  which 

the  spinal  cord  passes. 
Fron'tal  bone :  the  bone  forming  the  front  of  the  skull. 
Func'tion  (Lat.  functio,  trom  fungi,  to  perform) :  the  appropri^e  action 

of  any  organ  or  part  of  an  organism. 
Fun'gi-form  pa-pil'lae :  one  form  of  the  papillae  of  the  tongue. 

Gan'gli-on  (Lat.,  a  sort  of  swelling  or  excrescence,  from  Gr.)  :  a  little 
knot  of  nervous  matter  composed  mainly  of  nerve  cells. 

Gas'tric  (Gr.  gaster,  stomach)  :  pertaining  to  the  stomach,'or  situated 
near  it;  as  the  gastric  juice,  the  gastric  artery. 

Gas-troc-ne'mi-us  (Gr.  gastroknemia,  the  calf  of  the  leg) :  the  chief 
muscle  of  the  calf  of  the  leg. 

Gland  (Lat.  glans,  glandis,  acorn)  :  an  organ  for  secreting  something 
to  be  used  in  or  eliminated  from  the  body. 

Glo-mer'u-lus  (Lat.,  diminutive  of  glomus,  ball)  :  one  of  the  little 
bunches  of  looped  capillary  blood  vessels  in  the  cortex  of  the  kid- 
ney, from  which  the  uriniferous  tubules  arise. 

Glos-so-phar-yn-ge'al  nerves  (Gr.  glossa,  tongue,  and  'Eng. pharyngeal) : 
the  ninth  pair  of  cranial  nerves. 

Glot'tis  (Gr.,  from  glotta,  the  tongue)  :  the  opening  from  the  pharynx 
into  the  larynx. 


GLOSSARY  379 

Gly'co-gen  (Gr.  glukus,  sweet,  and  -gen,  producing)  :  a  substance 
belonging  to  the  carbohydrates,  found  in  animal  tissues,  and 
especially  in  the  liver.  It  is  believed  to  be  deposited  as  a  reserve 
material  in  the  liver,  and  is  converted  into  sugar  as  required.  It 
is  sometimes  called  "  animal  starch." 

Goi'ter  (Fr.,  from  Lat.  guttur,  throat) :  a  disease  which  causes  an 
enlargement  of  the  thyroid  gland. 

Hair  f ol'li-cle  (La.t.  folliculus,  a  small  bag)  :  a  little  pit  or  depression 
in  the  skin,  from  the  bottom  of  which  a  hau'  grows. 

Ha-ver'sian  canals  (named  from  Havers,  a  London  anatomist)  :  small 
channels  in  the  bones  through  which  the  blood  vessels  ramify. 

He'li-um  (Gr.  helios,  the  sun)  :  a  gaseous  element  identified  in  the 
sun's  corona  (hence  the  name)  long  ago,  and  now  proved  to  exist 
in  the  earth's  atmosphere,  and  in  certain  minerals  of  our  planet. 

Hem-0-glo'bin  (Gr.  haima,  blood,  and  Lat.  globus,  a  ball)  :  the  coloring 
matter  of  the  red  corpuscles  of  the  blood. 

He-pat'ic  (Gr.  hepatiJcos,  of  the  liver)  :  pertaining  in  any  way  to  the 
liver,  as  the  hepatic  artery. 

His-to-log'ic-al  (Gr.  Jiistos,  a  web,  and  logia,  speech)  :  pertaining  to 
histology,  which  is  that  branch  of  anatomy  concerned  with  the 
minute,  especially  the  microscopic,  structure  of  the  tissues. 

Hu'me-rus  (Lat.,  the  shoulder)  :  the  bone  of  the  upper  arm. 

Hy'a-line  (Gr.  hucdos,  glass)  :  resembling  glass  ;  transparent,  as  hya- 
line cartilage. 

Hy'dro-gen  (Gr.  hudor,  water,  and  -gen,  producing)  :  one  of  the  chemi- 
cal elements;  a  very  light  gas.  It  unites  with  oxygen  to  form 
water. 

Hy'gi-ene  (Gr.  hugieia,  health)  :  that  department  of  knowledge  which 
concerns  the  preservation  of  health. 

Hy'oid  bone  (Gr.  Y,  the  letter  upsilon,  and  eidos,  form ;  from  the  shape 
of  the  bone)  :  the  bone  at  the  root  of  the  tongue. 

Hy-po-gas'tric  plexus  (Gr.  hupogastrion,  the  lower  part  of  the  abdo- 
men) :  a  nervous  network  lying  on  each  side  of  the  rectum. 

Hy-po-glos'sal  (Gr.  Jiupo,  under,  and  glossa,  tongue)  :  the  twelfth  pair 
of  cranial  nerves. 

Il-e-o-cae'cal  valve  (from  Ueum  and  ccecum)  :  the  valve  at  the  junction 
of  the  small  intestine  with  the  large  intestine.  It  prevents  the 
contents  of  the  latter  from  flowing  into  the  former. 


380  GLOSSARY 

Il'e-um  (Lat.,  gToin)  :  the  last  division  of  the  small  intestine. 

Il'i-ac  arteries  (Lat.  iHum,  the  flank)  :  the  arteries  supplying  the  pel- 
vis and  its  organs  and  the  legs. 

Im-mune'  (Lat.  immunis,  free,  exempt)  :  exempt  from  a  certain  dis- 
ease by  nature,  from  inoculation,  or  from  a  previous  attack. 

In-ci'sors  (Lat.  incidere,  to  cut  in)  :  the  eight  front  teeth. 

In'cus  (Lat.,  anvil)  :  the  middle  one  of  the  auditory  ossicles,  named 
from  its  anvil-like  shape. 

In-flam-ma'tion  (Lat.  injiammatio)  :  a  diseased  condition  of  a  part  of 
the  body,  shown  by  excess  of  blood,  swelling,  and  extra  heat. 

In-hi-bi'tion  (Lat.  mhibere,  to  restrain)  :  the  lowering  or  restraining 
of  the  action  of  a  nervous  mechanism  by  nervous  impulses  from 
a  connected  mechanism. 

In-hib'i-to-ry :  restraining. 

In-nom'in-ate  artery  (Lat.  innom'matus,  nameless)  :  one  of  the  great 
arteries  rising  from  the  arch  of  the  aorta.  It  soon  divides  into  the 
right  subclavian  and  the  right  common  carotid  artery. 

In-OC-U-la'tion  (Lat.  inoculare,  to  ingraft)  :  the  introduction  of  the 
germs  of  a  disease  through  the  skin,  so  as  to  give  the  disease. 

In-spi-ra'tion  (Lat.  in,  in,  and  spirare,  to  breathe)  :  the  act  of  breath- 
ing in. 

In'su-la  (Lat.,  an  island)  :  a  portion  of  the  cortex  of  the  brain  lying 
beneath  the  Sylvian  fissure  ;  also  called  the  isla7id  of  Reil. 

In-ter-cos'tal  (Lat.  inter,  between,  and  costa,  rib)  :  between  the  ribs. 

In-tes'tin-al  juice :  the  fluid  secreted  by  the  glands  of  the  intestine. 
It  plays  some  part  in  the  digestive  process. 

In-tes'tine  (Lat.  intestinum)  :  the  long  tube  leading  from  the  stomach 
to  the  anus ;  the  bowels. 

In-tra-cen'tral  nerves  (Lat.  intra,  within)  :  those  nerves  which  form 
lines  of  communication  between  the  various  nerve  centers,  as  dif- 
ferent parts  of  the  brain  and  spinal  cord. 

In-ver'te-brates  (Lat.  in-,  without,  and  vertebratus,  vertebrate):  ani- 
mals having  no  internal  vertebral  column. 

I'ris  (Gr.  and  Lat.,  the  rainbow)  :  the  colored  portion  of  the  eye,  hav- 
ing in  its  center  the  pupil. 

Ir-ri-ta-bil'i-ty  (Lat.  irritare,\.o  excite)  :  the  power  possessed  by  living 
cells  of  reacting  under  stimulus. 

Je-ju'num  (Lat.,  empty) :  the  middle  portion  of  the  small  intestine, 
between  the  duodenum  and  the  ileum. 


GLOSSARY  381 

Ju'gU-lar  vein  (Lsit.  j ugulum,  collar  bone,  diminutive  oijugum,  yoke)  : 
one  of  the  two  large  veins  of  the  throat. 

Ka-tab'o-lism  (Gr.  kata,  down,  and  ballein,  to  throw)  :  the  deRtructive 

processes  of  the  body;  opposed  to  anabolism. 
Kid'neys  :  glandular  structures  lying  in  the  loins  opposite  the  lumbar 

vertebrae.     Their  function  is  the  purification  of  the  blood  by  the 

excretion  of  urine. 

Lab'y-rinth  (Lat.  labyrinthus,  a  structure  having  many  intricate  pas- 
sages) :  the  internal  ear. 

Lach'ry-mal  gland  (Lat.  lacrima,  tear)  :  the  gland  which  secretes 
the  tears. 

Lac'te-als  (Lat.  lacteus,  milky) :  the  lymphatic  vessels  w^hich  convey 
the  chyle  from  the  alimentary  canal  to  the  thoracic  duct ;  so  called 
from  the  color  of  the  chyle. 

Ld-cu'nae  (Sing,  lacuna,  Lat.,  a  pit)  :  microscopic  cavities  in  bone 
occupied  by  the  bone  cells. 

La-mel'lae  (Sing,  lamella,  Lat.,  a  small  plate  of  metal)  :  layers  of 
bone  tissue  arranged  around  the  Haversian  canals. 

Lar'ynx  (Gr.  larugx)  :  the  enlarged  upper  end  of  the  windpipe,  con- 
taining the  vocal  cords. 

Lig'a-ment  (Lat.  ligare,  to  bind)  :  a  band  of  connective  tissue  bind- 
ing one  part  to  another. 

Liv'er:  a  large  gland  lying  below  the  diaphragm  on  the  right  side. 
It  secretes  bile  and  performs  other  functions  in  metabolism. 

Lum'bar  (Lato  lumbus,  loin)  :  pertaining  to  or  near  the  loins ;  as  the 
lumbar  arteries. 

Lymph  (Lat.  lympha,  clear  water,  a  fountain)  :  a  colorless  fluid  filling 
the  lymphatics  and  lymph  spaces.  It  consists  mostly  of  the  fluid 
part  of  blood. 

Lym-phat'ics :  small  transparent  tubes  arising  in  the  tissues  and  con- 
veying lymph. 

Mag-ne'si-um  :  a  light,  silver-white  metal. 

Ma'lar  bones  (Lat.  mala,  the  cheek  bone,  cheek)  ;  the  bones  of  the 
cheek. 

Mal'le-us  (Lat.,  a  hammer)  :  the  outer  of  the  three  auditory  ossicles, 
named  from  its  shape. 

Mam'mal  (Lat.  mamma,  the  breast)  :  an  animal  of  the  class  mam- 
malia, the  highest  class  of  vertebrates,  containing  all  those  which 
suckle  their  young. 

macy's  phys. — 24 


382  GLOSSARY 

Ma-nom'e-ter  (Gr.  manos,  thin,  and  metron,  a  measure)  :  an  instru- 
ment for  measuring  the  pressure  of  gases  and  liquids. 

Master  tissues :  those  tissues  of  the  body  which  have  to  do  with  the 
liberation  of  energy,  viz.  the  muscular  and  nervous  tissues. 

Mas-ti-ca'tion  (Lat.  masticare,  to  chew) :  the  act  of  chewing  the  food. 

Matter :  that  of  which  the  sensible  universe  and  all  bodies  are  com- 
posed ;  anything  which  occupies  [space  or  is  perceptible  to  the 
senses. 

Max'il-la-ry  bones  (Lat.  maxilla,  jaw)  :  the  bones  of  the  jaws. 

Me-a'tus  (Lat.,  a  passage,  from  meare,  to  go)  :  a  natural  passage  or 
canal.  The  auditory  meatus  is  a  tube  of  cartilage  continuous  with 
the  pinna  of  the  ear,  and  leading  to  the  membrane  of  the  tym- 
panum. 

Me-dulla  (Lat.,  marrow)  :  a  synonym  for  medulla  oblongata.  The 
term  is  also  applied  to  the  marrow  of  bones,  and  to  the  deep  inner 
portions  of  the  kidneys  and  other  organs. 

Medulla  ob-lon-ga'ta  (Lat.)  :  the  hindmost  segment  of  the  brain, 
continuous  wdth  the  spinal  cord. 

Med'ul-la-ry  cav-i-ty  (Lat.  medulla,  marrow)  :  the  cavity  in  a  bone 
which  contains  marrow. 

Medullary  sheath :  the  layer  of  white  matter  immediately  surround- 
ing the  axis  cylinder  of  a  nerve. 

Me-dul'la-ted :  having  the  medullary  sheath. 

Mem'bra-nous  coch'le-a:  a  membranous  tube  of  the  internal  ear; 
also  called  the  cochlear  canal. 

Membranous  lab'y-rinth:  a  closed  sac  of  membrane  lying  in  the 
bony  labyrinth  of  the  ear. 

Mes'en-ter-y  (Gr.  mesenterion,  literally,  the   middle  intestine)  :   the 
membrane  or  one  of  the  membranes  which  connect  the  intestines . 
and  their   appendages  with   the  hinder  wall   of  the   abdominal 
cavity. 

Me-tab'o-lism  (Gr.  metahole,  change)  :  the  processes  by  which  living 
cells  transform  into  their  own  proper  substance  material  brought 
by  the  blood,  and  also  break  down  and  prepare  for  excretion 
matter  which  has  fulfilled  its  function  ;  anabolism  and  katabolism. 

Met-a-car'pus  (Gr.  meta,  beyond,  and  karpos,  the  wrist)  :  the  part  of 
the  skeleton  between  the  wrist  and  the  fingers,  consisting  of  five 
bones. 

Met-a-tar'sus  (Gr.  meta,  beyond,  between,  and  tarsos,  the  flat  of  the 
foot)  :  that  part  of  the  skeleton  between  the  ankle  and  the  toes. 


GLOSSARY  383 

Mi'crobe  (Gr.  mikros,  little,  and  bios,  life)  :  a  microscopic  organism ; 
especially  one  of  those  forms  which  produce  disease. 

Mi'tral  valves :  the  bicuspid  valves  of  the  heart,  which  are  shaped 
like  a  miter. 

Molars  (Lat.  molere,  to  grind)  :  the  three  back  teeth  on  each  side  of 
each  jaw. 

Mol'e-cule  (Lat.  molecula,  diminutive  of  moles,  a  mass)  :  the  smallest 
part  into  which  a  substance  can  be  divided  without  destroying  its 
chemical  character. 

Mo'tor  areas :  those  portions  of  the  cortex  of  the  brain  whose  stimu- 
lation results  in  motion. 

Motor  nerves :  nerves  whose  function  it  is  to  excite  muscular  contraction. 

Mu'cous  membrane  (Lat.  mucus,  slime,  and  membrana,  a  skin,  parch- 
ment) :  the  lining  membrane  of  all  passages  and  cavities  of  the 
body  which  have  an  external  communication. 

Mu'cus  (Lat.,  slime)  :  a  fluid  secreted  by  the  mucous  membrane. 

Mus'cu-lar  sense:  impressions  conveyed  by  sensory  nerve  fibers 
running  from  the  muscles  to  the  spinal  cord  and  thence  to  the 
brain,  giving  information  of  the  general  condition  of  the  muscles, 
and  helping  to  form  judgments  of  weight,  pressure,  etc. 

Nar-COt'ic  (Gr.  narkotikos,  making  numb)  :  a  substance  which  blunts 
the  sensibilities,  induces  sleep,  and,  in  large  quantities,  complete 
insensibility. 

Nerv'ous  impulse :  the  molecular  disturbance  which  is  conveyed  by 
the  nerve  fibers  from  the  point  of  stimulation  to  the  nervous  center 
in  the  brain  or  spinal  cord,  or  from  a  nerve  center  to  a  muscle. 

Neu'ral  arch  (Gr.  neuron,  nerve)  :  the  arch  of  a  vertebra  which  incloses 
and  protects  the  corresponding  part  of  the  spinal  cord. 

Neu-rax'on  :  the  axis  cylinder  of  a  nerve  fiber. 

Neu-ri-lem'ma  (Gr.  neuron,  nerve,  and  lemma,  a  husk) :  the  primitive 
sheath,  or  inclosing  membrane,  of  a  nerve  fiber. 

Neu-rog'li-a  (Gr.  neuron,  nerve,  and  glia,  glue)  :  a  peculiar  supporting 
tissue  of  the  nervous  system. 

Neu'ron  (Gr.,  nerve)  :  the  nerve  unit,  consisting  of  a  nerve  cell  with 
its  processes,  one  of  which  becomes  the  axis  cylinder  of  a  nerve 
fiber.     Of  such  units  the  whole  nervous  system  is  composed. 

Ni'tro-gen  (Lat.  nitrum,  natron,  and  -gen,  producing)  :  a  gaseous  ele- 
ment forming  four  fifths  of  the  atmosphere,  and  found  in  many 
important  compounds. 


384  GLOSSARY 

Non-me-dul'la-ted :  without  the  medullary  sheath,  as  nonmedullated 

nerves. 
Nu-cle-o'lus  (Lat.,  diminutive  of  nucleus,  a  little  nut)  :  the  nucleus  of 

a  nucleus. 
Nu'cle-us  (Lat.,  a  little  nut)  :  a  central  modified  mass  of  protoplasm 

found  in  nearly  all  cells. 
Nu-tri'tion  (Lat.  nutrire,  to  nourish)  :  a  term  which,  in  its  broad  sense, 

includes  all  the  processes  concerned  in  the  growth,* maintenance, 

and  repair  of  the  living  body  and  all  its  parts. 

Oc-cip'i-tal  (Lat.  occiput,  the  back  of  the  head)  :  pertaining  to  the 
hinder  part  of  the  head,  as  the  occipital  lobe  of  the  brain. 

Oc-u-lo-mo'tor  (Lat.  oculus,  the  eye)  :  pertaining  to  the  movements  of 
the  eye ;  applied  especially  to  the  third  pair  of  cranial  nerves. 

0-don'toid  process  (Gr.  odontoeides,  tooth-shaped)  :  the  tooth  or  peg  of 
the  axis  or  second  cervical  vertebra. 

01-fac'to-ry  cells  (Lat.  olf actus,  from  olere,  to  have  a  smell,  and /accre, 
to  make)  :  the  cells  which  are  affected  by  odors;  the  end  organs 
for  smell,  in  the  lining  membrane  of  the  nasal  passages. 

Olfactory  nerves  :  the  nerves  of  smell,  distributed  from  the  olfactory 
bulb  over  the  membrane  lining  the  nasal  passages. 

Olfactory  tract :  the  band  of  nervous  matter  lying  between-the  olfac- 
tory bulbs  (from  which  the  oKactory  nerves  spread  out)  and  the 
roots  of  those  nerves  in  the  cerebrum. 

0-men'tum  (Lat.)  :  a  fold  of  the  peritoneum. 

O'pi-um  (Gr.  opion,  poppy  juice)  :  the  juice  of  the  poppy,  thick- 
ened into  a  sticky  brown  mass  of  bitter  taste  and  peculiar  odor. 
It  is  a  stimulant  narcotic,  and  powerfully  affects  the  central  nerv- 
ous system. 

Op'tic  (Gr.  optikos)  :  pertaining  to  sight. 

Optic  chi-as'ma  (Gr.,  two  lines  crossed)  :  the  crossing  of  the  optic 
nerves. 

Optic  com'mis-sure  (Lat.  con,  with,  and  mitiere,  missus,  to  place)  :  the 
union  of  the  optic  nerve  fibers  from  the  two  eyes,  after  passing 
through  the  openings  in  the  eye  sockets. 

Optic  thal'a-mus  (Lat.,  chamber)  :  masses  of  gray  matter  at  the  base 
of  the  cerebrum. 

Or'bit  (Lat.  orbis,  circle)  :  eye  socket. 

Or'gan  (Gr.  organon,  an  instrument)  :  one  of  the  parts  or  members 
of  a  body  which  has  some  specific  function  ;  as  the  organ  of  vision. 


GLOSSARY  385 

Organ  of  Cor'ti  (named  from  Corti,  an  Italian  scientist)  :  an  epithelial 
structure  within  the  membranous  cochlea  believed  to  contain  the 
end  organs  for  hearing. 

Os  in-nom-i-na'tum  (Lat.,  nameless  bone)  :  the  hip  bone. 

Os-mo'sis  (Gr.  osmos,  impulsion,  pushing) :  the  diffusion  of  fluids 
through  membranes. 

Os'se-OUS  (Lat.  os,  bone)  :  bony,  made  of  bone;  as  osseous  tissue. 

Os-si-fi-ca'tion :  the  process  of  changing  into  bone. 

O'to-liths  (Gr.  ous,  otos,  ear,  and  lithos,  stone)  :  minute  hard  particles 
in  the  passages  of  the  inner  ear. 

Ox-i-da'tion  :  the  chemical  union  of  oxygen  with  other  substances,  as 
in  combustion. 

Ox-y-gen  (Gr.  oxus,  sharp,  acid,  and  -gen,  producing,  because  errone- 
ously supposed  to  be  present  in  all  acids)  :  a  gaseous  chemical  ele- 
ment found  in  the  atmosphere  and  in  many  compounds. 

Ox-y-hem-0-glo'bin  :  hemoglobin  which  has  united  with  oxygen. 

Pa-cin'i-an  corpuscles  (named  from  Pacini,  an  Italian  physician)  : 
one  of  the  forms  of  touch  end  organs. 

Pal'ate  (Lat.  palatinn)  :  the  roof  of  the  mouth  and  floor  of  the  nose. 
The  soft  palate  is  a  fold  of  muscular  membrane  hanging  between 
the  back  part  of  the  mouth  and  the  upper  part  of  the  pharynx. 

Pan'cre-as  (Gr.  pan,  all,  and  kreas,  flesh)  :  a  gland  in  the  abdomen 
near  the  stomach.  It  pours  its  secretion  into  the  duodenum.  In 
animals  it  is  called  siveetbread. 

Pan-cre-at'ic  juice :  the  secretion  of  the  pancreas  which  acts  upon  the 
fats  and  proteids  in  the  food. 

Pa-pil'la  (Lat.,  a  nipple)  :  a  minute,  rounded  projection  ;  as  the  papillae 
of  the  tongue. 

Pap'il-la-ry  muscles :  muscular  bundles  within  the  ventricles  of  the 
heart,  attached  to  the  heart  walls  and,  by  the  tendinous  cords,  to 
the  valves  between  the  auricles  and  the  ventricles. 

Pa-ri'e-tal  bones  {L-Ai.  paries,  wall)  :  bones  of  the  cranium  forming  a 
part  of  the  top  and  sides  of  the  skull. 

Pa-rot'id  glands  (Gr.  para,  near,  and  ous,  otos,  ear)  :  the  salivary 
glands  near  the  ears. 

Pa-tel'la  (Lat.,  a  small  pan  or  dish)  :  the  knee  pan. 

Pec'to-ralgirdle  (L,a,t.  pectoralis,  pertaining  to  the  breast)  :  the  clavi- 
cle and  scapula  upon  each  side,  to  which  are  attached  the  bones  of 
•  the  upper  arms. 


386  GLOSSARY 

Pe-dun'cle:  a  band  of  nervous  matter  connecting  different  parts  of 
the  brain. 

Pel'vic  girdle  (Lat.  pelvis,  a  basin)  :  the  two  bones,  one  upon  each 
side,  called  the  os  innominatum,  to  which  are  attached  the  bones  of 
the  upper  legs. 

Pel'vis  (Lat.,  a  basin)  :  the  pelvic  girdle  and  sacrum. 

Pep'sin  (Gr.  pepsis,  cooking,  digestion)  :  a  ferment  found  in  the  gas- 
tric juice. 

Per-i-car'di-um  (Gr.  pericardion,  around  the  heart) :  the  serous  mem- 
brane which  surrounds  the  heart. 

Per-i-mys'i-um  (Gr.  peri,  around,  and  mus,  muscle)  :  the  sheath  of 
areolar  tissue  which  surrounds  a  bundle  of  muscle  fibers. 

Per-i-neu'ri-um  (Gr.  j)eri,  around,  and  neuron,  nerve)  :  the  membra- 
nous sheath  surrounding  a  nerve. 

Per-i-os'te-um  (Gr.  peri,  around,  and  osteon,  bone)  :  the  membrane 
surrounding  a  bone. 

Pe-riph'er-al  (Lat.  periplieria,  from  Gr.  peri,  around,  and  pherein,  to 
bear,  carry)  :  belonging  to  the  outside  or  superficial  portions  of  a 
body. 

Per-i-stal'tic  (Gr.  peri,  around,  and  stellein,  to  set,  place) :  pertaining 
to  the  waves  of  contraction,  called  peristalsis,  running  down  the 
alimentary  canal  to  force  on  the  contents. 

Per-i-to-ne'um  (Gr.  j)eri,  around,  and  teinein,  to  stretch) :  the  serous 
membrane  lining  the  abdominal  cavity. 

Per-spi-ra'tion  (Lat.  jyer,  through,  and  spirare,  to  breathe):  liquid 
excretion  from  the  skin,  mainly  from  sweat  glands. 

Pha-lan'ges  (Lat.,  plural  of  phalanx,  a  body  of  troops  in  ranks  and 
files,  from  Gr.  phalagx)  :  the  bones  of  the  fingers  and  toes. 

Phar'ynx  (Gr.  pharugx,th.e,  throat)  :  that  part  of  the  alimentary  canal 
between  the  cavity  of  the  mouth  and  the  esophagus. 

Phos'phate :  a  chemical  compound  of  phosphoric  acid  with  a  base. 

Phos'pho-rus  (Gr.  pJios,  light,  and  pherein,  to  bring)  :  a  chemical  ele- 
ment ;  a  white  or  yellowish  waxy  solid  that  gives  off  a  faint  glow. 

Phre'nic  ((xr.  j)hren,  the  diaphragm)  :  belonging  to  the  diaphragm  ;  as 
the  phrenic  artery  or  nerve. 

Phys-i-ol'o-gy  (Gr.  phusis,  nature,  and  logia,  discourse)  :  the  science 
which  treats  of  the  phenomena  of  living  organisms.  It  is  divided 
into  animal  and  vegetable  physiology. 

Pi'a  ma'ter  (Lat.,  kind,  tender  mother)  :  the  delicate  vascular  mem- 
brane immediately  covering  the  brain  and  spinal  cord. 


GLOSSARY  387 

Pi'ne-al  body  (Lat.  plnea,  a  pine  cone)  :  a  glandlike  body  in  the  roof 
of  the  third  ventricle,  of  the  brain. 

Pin'na  (Lat.,  a  feather)  :  the  folded  sheet  of  cartilage  which  forms 
the  principal  part  of  the  external  ear. 

Pithed :  deprived  of  the  central  nervous  system  by  the  passing  of  a 
wire  or  needle  through  the  vertebral  canal. 

Plas'ma  (Lat.  and  Gr.,  anything  formed  or  molded)  :  the  colorless 
fluid  of  the  blood. 

Pleu'ra  (Gr.,  a  rib,  the  side)  :  the  serous  membrane  which  covers  the 
lungs  and  lines  the  cavity  of  the  thorax. 

Plex'us  (Lat.,  a  twining,  braid,  from  plectere^  to  braid,  twine)  :  a  net- 
work of  vessels,  nerves,  or  fibers. 

Pons  Va-roli-i  (Lat.,  bridge  of  Varoli  —  an  Italian  anatomist):  a 
band  of  nervous  tissue  on  the  front  or  ventral  side  of  the  medulla 
oblongata,  connecting  the  two  sides  of  the  cerebellum. 

Pop-lit'e-al  (Lat.  poples,  the  ham)  :  pertaining  to  the  ham  or  back  of 
the  knee,  as  the  popliteal  artery  or  ligament. 

Por'tal  circulation  (Lat.  porta,  gate)  :  the  passage  of  venous  blood 
from  the  capillaries  of  one  organ  to  those  of  another  before  reach- 
ing the  heart.     In  man,  the  circulation  of  the  liver. 

Portal  vein :  the  large  vein  of  the  liver,  bringing  blood  to  its  capil- 
laries. 

Pos-te'ri-or  (Lat.,  coming  after)  :  away  from  the  head,  or  sometimes, 
in  human  physiology,  toward  the  back. 

Po-tas'si-um  (Lng.  potash)  :  a  chemical  element,  found  only  in  com- 
bination with  acids. 

Prim'i-tive  sheath :  the  inclosing  membrane  of  a  nerve  fiber. 

Proc'ess  (Lat.  processus,  a  going  forward):  an  outgrowth;  a  projec- 
tion, as  the  spinous  process  of  a  vertebra. 

Pro'te-ids  (Gr.  protos,  first)  :  the  food  elements  which  form  tissue. 

Pro'to-plasm  (Gr.  protos,  first,  and  plasma,  anything  formed)  :  an 
albuminoid  substance  consisting  of  carbon,  oxygen,  nitrogen,  and 
hydrogen ;  capable  under  proper  conditions  of  manifesting  certain 
phenomena  of  life ;  "  the  physical  basis  of  life."" 

Pty'a-lin  (Gr.  ptnalon,  spittle)  :  the  peculiar  principle  of  saliva  which 
acts  as  a  ferment  on  starch,  converting  it  into  dextrose,  a  variety 
of  sugar. 

Pul'mo-na-ry  (Lat.  pulmo,  a  lung)  :  pertaining  to  the  lungs,  as  the 
pulmonary  arteries,  which  carry  blood  from  the  heart  to  the 
Jungs. 


388  GLOSSARY 

Pulmonary  circulation :  the  circulation  of  the  blood  from  the  right 

ventricle  of  the  heart  through  the  pulmonary  arteries,  capillaries, 

and  veins  back  to  the  left  auricle. 
Pu'pil  (L^t.  pupilla)  :  the  round  opening  in  the  center  of  the  iris. 
Pu-tre-fac'tion  (Lat.  putrefactio) :  the  ofensive  decay  of  albuminous 

and  other  matter. 
Py-lo'rus  (Gr.  puloros,  gate  keeper) :  the  opening  from  the  stomach 

into  the  intestine. 

Ra'di-ant  energy  (Lat.  radiare,  to  emit  rays)  :  the  force  resident  in 
vibrations  of  the  ether  which  fills  all  space. 

Ra'di-us  (Lat.,  a  staff,  rod,  ray)  :  one  of  the  bones  of  the  forearm. 

Rec'tum  (Lat.  rectus,  straight)  :  the  last  division  of  the  large  intes- 
tine, and  hence  of  the  alimentary  canal. 

Re'flex  action  (Lat.  rejlectere,  rejlexus,  to  bend  back)  :  action  in 
which  afferent  impulses  reach  a  nerve  center  and  efferent  impulses 
are  sent  back  without  the  higher  brain  centers  having  been  stimu- 
lated.    Such  action  is  involuntary  and  often  unconscious. 

Re-frac'tion-  (Lat.  refrangere,  refractus,  to  break)  :  the  change  in 
the  direction  of  a  ray  of  light  in  passing  from  one  medium  to  an- 
other of  a  different  density. 

Re'nal  (Lat.  renes,  kidneys)  :  pertaining  to  or  in  the  region  of  the 
kidneys,  as  the  renal  artery,  the  renal  plexus. 

Ren'nin  (Anglo-Saxon  rinnan,  to  run)  :  that  ferment  in  the  gastric 
juice  which  causes  milk  to  curdle ;  the  element  in  rennet  which 
assists  in  the  making  of  cheese. 

Re-pro-duc'tion  (Lat.  reproducere,  to  produce  again)  :  the  process  by 
which  new  organisms  are  produced  from  those  already  existing. 

Res'o-na-ting  cavities  (Lat.  resonare,  to  sound  back,  echo) :  the 
pharynx,  mouth,  and  nasal  cavities,  slight  changes  in  which 
modify  the  sound  of  the  voice. 

Res-pi-ra'tion  (Lat.  respirare,  to  breathe)  :  the  act  of  taking  in  and 
giving  out  air. 

Re-spir'a-to-ry  center :  that  cluster  of  nerve  cells  in  the  medulla  ob- 
longata which  controls  and  coordinates  the  movements  of  the 
muscles  concerned  in  breathing. 

Ret'i-na  (Lat.  rete,  a  net)  :  that  membrane  of  the  eye  in  which  the 
fibers  from  the  optic  nerve  terminate. 

Rhyth'mic  (Gr.  rhufhmos,  measured  motion)  :  characterized  by  a  regu- 
lar succession  of   movements,  impulses,  or  sounds. 


GLOSSARY  389 

Rick'ets :  a  disease  of  early  life  characterized  by  defective  nutrition 
of  the  bones,  and  often  due  to  a  lack  of  proper  food. 

Ri'gor  mor'tis  (Lat.,  rigidity  of  death)  :  the  condition  in  a  dead  ani- 
mal body  due  to  a  coagulation  of  the  protoplasm  of  the  muscle 
cells. 

Rods  of  Cor'ti :  pillarlike  cells  forming  part  of  the  organ  of  Corti  in 
the  inner  ear. 

Sac'cule  (Lat.  sacculus,  a  little  sac)  :  part  of  the  membranous  laby- 
rinth of  the  ear. 

Sa'crum  (Lat.  sacer,  sacred)  :  the  lower  part  of  the  spine,  immedi- 
ately above  the  coccyx. 

Sa-li'va  (Lat.,  spittle)  :  the  mixed  secretions  of  the  salivary  glands 
and  the  mucous  membrane  of  the  mouth. 

Sal'i-va-ry  glands  :  the  parotid,  submaxillary,  and  sublingual  glands 
which  pour  their  secretions  into  the  mouth. 

Salt :  a  chemical  compound  formed  by  uniting  an  acid  with  a  base. 
The  salts  which  are  food  elements  are  chiefly  chlorides,  phosphates, 
and  carbonates  of  sodium,  potassium,  calcium,  and  magnesium, 
with  salts  of  iron  and  some  organic  acids. 

Sar-co-lem'ma  (Gr.  sarx,  flesh,  and  lemma,  a  husk)  :  the  membrane 
surrounding  a  striped  muscular  fiber. 

Scap'u-la  (Lat.)  :  the  shoulder  blade. 

Sci-at'ic  nerve  (Lat.  sclaticus)  :  the  nerve  of  the  hip  and  thigh. 

Scle-rot'ic  (Gr.  skleros,  hard)  :  the  outer  coat  of  the  eye. 

Se-ba'ceous  glands  (Lat.  sebaceus,  from  sebum,  tallow)  :  small  glands 
under  the  skin  which  secrete  an  oily  matter  which  softens  and 
lubricates  hair  and  skin. 

Se-cre'tiOn  (Lat.  secretio,  the  act  of  secreting)  :  the  process  by  which 
the  various  glands  separate  material  from  the  blood  and  elaborate 
it  into  new  substances  so  as  to  form  the  various  secretions,  as  bile, 
saliva,  etc. 

Se-cre'to-ry  nerves :  nerves  that  supply  the  organs  of  secretion. 

Sem-i-cir'cu-lar  canals  :  three  half-circular  canals  of  the  internal  ear. 

Sem-i-lu'nar  valves  (Lat.  seini-,  half,  and  lunaris,  from  luna,  the 
moon)  :  valves  of  the  heart,  at  the  beginning  of  the  aorta  and  of 
the  pulmonary  artery,  which  prevent  the  blood  from  flowing  back 
into  the  ventricle. 

Sen'so-ry  areas :  those  portions  of  the  brain  whose  stimulation  re- 
sults in  sensation. 


390  GLOSSARY 

Sensory  nerves  :  nerves  which  carry  impulses  resulting  in  sensation. 
Se'rous  :  pertaining  to  serum  ;  filled  with,  or  secreting  serum. 
Se'rum  (Lat.,  akin  to  Gr.  o7'os,  Skr.  sara,  curd)  :  the  watery  portion 

of  certain  animal  fluids,  as  blood,  milk,  etc. 
Skull :  the  skeleton  of  the  head. 
So'di-um   (Eug.    soda)  :    a   chemical  element   found   in   union   with 

various  acids. 
So'lar  plexus :  a  network  of  nerves  about  the  pit  of  the  stomach, 

containing  fibers  from  many  different  nerves. 
Spec'trum  (Lat.,  an  appearance,  image)  :  the  several  rays  of  which 

light  is  composed  separated  by  refraction  and  spread  out  in  a  band 

of  colors  and  dark  lines. 
Sphe'noid   (Gr.  sphenoeides,  wedge-shaped)  :    an   irregularly  shaped 

bone  in  front  of  the  occipital  in  the  base  of  the  skull. 
Sphinc'ter   (Gr.  sphigktei^,  anything  which  binds   tight)  :    a  muscle 

which  surrounds  and  tends  to  close  a  natural  opening. 
Spi'nal  (Lat.  spina,  the  spine)  :  pertaining  to  the  backbone. 
Spinal  ac-ces'so-ry  nerves :  the  eleventh  pair  of  cranial  nerves. 
Spinal  cord :  the  cord  of  nervous  matter  lying  in  the  channel  of  the 

vertebral  column,  and  continuous  with  the  nervous  matter  of  the 

brain. 
Spiral  ganglion :  a  mass  of  nerve  cells  in  the  inner  ear. 
Spleen :  one  of  the  ductless  glands,  lying  in  the  abdomen  near  the 

stomach.     Of  its  functions  little  is  positively  known. 
Spleen  pulp  :  a  soft  substance  in  the  meshes  of  the  tissue  of  the  spleen. 
Splen'ic  :  pertaining  to  the  spleen  ;  as  the  splenic  vein. 
Spu'tum  (Lat.,  from  spuere,  to  spit) :  that  which  is  expectorated  or 

discharged  from  the  lungs. 
Sta'pes   (Lat.,   a  stirrup)  :    the   innermost  of   the  auditory  ossicles, 

shaped  like  a  stirrup. 
Ster'il-ize  (Lat.  sterilis,  barren)  :  to  render  incapable  of  germination ; 

to  make  sterile ;  to  destroy  the  germs  in  food  or  water. 
Ster'num  (Gr.  sternon,  the  breast)  :  the  bone  in  the  middle  of  the  front 

of  the  chest. 
Stim'u-lus  (Lat.  for  stigmulus,  akin  to  instigare,  to  prick,  to  goad) : 

any  substance  or  agent  capable  of  arousing  the  activity  of  a  nerve 

or  irritable  muscle,  or  capable  of  producing  an  impression  upon  a 

sensory  organ. 
Stro'ma  (Gr.,  a  couch)  :  the  colorless  framework  of  a  red  blood  cor- 
puscle or  other  cell. 


GLOSSARY  391 

Sub-cla'vi-an  (Lat.  sub,  under,  below)  :  situated  below  the  clavicle,  as 
the  subclavian  arteries  or  veins. 

Sub-lin'gual  glands  :  the  salivary  glands  under  the  tongue. 

Sub-max'il-la-ry  glands  :  the  salivary  glands  under  the  jaw. 

Su-pra-re'nal  cap'sules  (Lat.  supra,  above)  :  two  small  bodies  situated 
upon  the  kidneys.     Their  function  is  unknown. 

Sus-pen'so-ry  ligament  (Lat.  suspendere,  suspensum,  to  suspend)  :  a 
ligament  attached  to  the  crystalline  lens  and  the  ciliary  processes 
of  the  eye.     It  assists  in  accommodation. 

Su'ture  (Lat.  sutura,  a  seam)  :  an  immovable  articulation,  as  one  of 
those  between  the  bones  of  the  skull. 

Syl'vi-an  fissure  :  the  furrow  which  divides  the  frontal  from  the 
temporal  lobe  of  the  brain ;  named  from  a  famous  anatomist 
Dubois,  or  Sylvius  (the  Latin  form  of  the  name). 

Sym-pa-thet'ic  nervous  system:  the  double  chain  of  ganglia  lying 
on  each  side  of  the  spinal  column,  with  the  nerves  issuing  there- 
from, the  plexuses  which  they  form,  and  the  small  ganglia  along 
their  course. 

Syn-o'vi-al  (Gr.  sun,  together,  and  Lat.  ovum,  Qgg)  :  of  or  pertaining 
to  synovia,  the  fluid  secreted  by  a  synovial  membrane  and  named 
from  its  resemblance  to  the  white  of  egg. 

Sys-tem'ic  circulation  :  the  general  circulation  of  the  blood  through- 
out the  body ;  opposed  to  the  restricted  pulmonary  circulation. 

Tar'sus  (Gr.  tarsos,  the  flat  of  the  foot)  :  the  ankle. 

Taste  buds  :  end  organs  for  taste  found  in  certain  papill?e  of  the  tongue. 

Tem'po-ral  bones  (Lat.  tempora,  the  temples)  :  complex  bones  situated 
in  the  side  of  the  head,  and  containing  the  internal  parts  of  the  ear. 

Temporal  lobe :  the  part  of  the  cerebrum  lying  on  each  side  just 
beneath  the  temporal  bone. 

Ten'don  (Lat.  tendere,  to  stretch)  :  a  band  or  layer  of  dense  fibrous 
tissue  at  the  end  of  a  muscle,  attaching  it  to  a  bone,  or  between 
two  muscular  bellies  ;  a  sinew. 

Tet'a-nus  (Gr.  tetanos,  spasm)  :  a  gentle,  continuous  vibration,  or  pro- 
longed contraction,  as  of  a  muscle  or  a  nerve. 

Tho-rac'ic  duct  (see  Thorax)  :  a  large  lymphatic  vessel  running 
upward  through  the  thorax  to  empty  into  the  jugular  vein. 

Tho'rax  (Lat.  and  Gr.,  a  breastplate,  or  the  part  of  the  body  covered 
by  a  breastplate)  :  that  part  of  the  body  between  the  neck  and  the 
abdomen,  and  containing  the  heart  and  the  lungs. 


392  GLOSSARY 

Thy'mus  gland  (Gr.  thumos,  the  sweetbread)  :  a  ductless  gland  in  the 

thorax  behmd  the  sternum.     Its  function  is  unknown. 
Thy'roid  cartilage  (Gr.  thureoeides,  shield-shaped)  :  a  sheet  of  carti- 
lage on  the  fiont  of  the  larynx. 
Thyroid  gland :  a  ductless  gland  of  unknown  function  in  the  region 

of  tlie  larynx. 
Tib'i-a  (Lat.)  :  the  inner  and  larger  of  the  two  bones  of  the  lower 

leg. 
Tis'sue :  one  of  the  materials  of  uniform  structure  forming  the  body, 

as  muscular  tissue. 
Ton'sil  (Lat.  tonsilla)  ;  one  of  a  pair  of  oval  bodies  situated  in  the 

recesses  on  each  side  of  the  fauces. 
Touch  corpuscles :  one  form  of  touch  end  organs. 
Tox'in  (Gr.  toxikon,  poison)  :   a  poisonous  kind  of  the  animal  base 

or  alkaloid  which  is  formed  in   the  putrefaction  of   albuminous 

matter. 
Tra'che-a  (Gr.  trachus,  rough)  :  the  windpipe. 
Trans'verse  ligament:    a  band  of  strong  tissue  dividing  the  large 

neural  ring  of  the  atlas  into  two  parts,  into  one  of  which  the  odon- 
toid process  fits. 
Tri'ceps  (Lat.,  having  three  heads,  from  tres,  three,  and  caput^  head)  : 

the  muscle  at  the  back  of  the  upper  arm. 
Tri-cus'pid   valves    (Lat.   tres,  three,  and  cuspis,  point)  :  the  valves 

guarding  the  opening  between  the  auricle  and  ventricle  on  the 

right  side  of  the  heart. 
Tri-gem'i-nal  nerves  (Lat.  trigeminus,  born  three  together)  :  the  fifth 

pair  of  cranial  nerves. 
Troch'le-ar  nerves  (Lat.  trochlea,  a  pulley)  :  the  fourth  pair  of  cranial 

nerves. 
Troph'ic  nerves   (Gr.    trophe,  nourishment)  :    nerves   which    directly 

influence  the  nutrition  of  the  tissues  to  which  tliey  go. 
Tu-ber'cu-lin :    a    liquid    prepared    from   cultures   of   the   tubercle- 

baciUus,  as  a  remedy  for  tuberculosis. 
Tu-ber-CU-lo'sis  (Lat.  luherculum,  diminutive  of  tuher,  tuber)  :  a  disease 

affecting  most  of  the  tissues,  and  characterized  by  the  formation  of 

tubercles  and  the  tubercle-bacillus. 
Tur'bi-nate  bones  (Lat.  turbinatus,  shaped  like  a  top  or  cone)  :  two 

small  bones  in  the  nostril  chambers. 
Tym'pa-num  (Lat.,  a  drum)  :  the  middle  ear.     The  membrane  of  the 
tympanum  is  the  eardrum. 


GLOSSARY  393 

Ul'na  (Lat.,  the  elbow)  :  the  inner  of  the  two  bones  of  the  fore  arm. 
U're-a  (Gr.  ouron,  urine,  originally  water)  :  a  crystalline  solid,  soluble 

in  water.     It  is  the  final  product  of  proteid  decomposition  in  the 

body,  and  the  chief  solid  constituent  of  the  urine. 
U-re'ter  (Gr.  oureter,  from  ouron,  urine)  :  the  excretory  duct  of  the 

kidney,  conveying  the  renal  excretion  to  the  bladder. 
U-ri-nif' er-ous  tu'bules  :  small  tubes  which  collect  the  urine  secreted 

in  the  cortex  of  the  kidneys. 
U'tri-cle  (Lat.  utriculus):  a  little  sac;  especially  the  little  sac  forming 

part  of  the  membranous  labyrinth  of  the  ear. 

Vac-ci-na'tion  ( Lat.  vacca,  cow)  :  inoculation  with  cowpox  virus  ob- 
tained directly  or  indirectly  from  the  cow. 

Va'gUS  (Lat.,  wandering)  :  the  tenth  pair  of  cranial  nerves. 

Val'vu-lae  con-ni-ven'tes  (Lat.  valva,  the  leaf  of  a  double  door;  con- 
nivere,  to  wink  at,  connive) :  the  semicircular  folds  in  the  lining 
membrane  of  the  small  intestine,  increasing  the  absorbing  surface. 

Vas'cu-lar  (Lat.  vasculum,  diminutive  of  vas,  vessel)  :  containing 
small  vessels  or  tubes,  as  the  vascular  system  for  the  circulation  of 
the  blood. 

Vas-o-con-strict'or  (Lat.  vas,  vessel,  and  Eng.  constrictor,  from  Lat. 
constringere,  to  draw  together)  :  causing  contraction  of  the  blood 
vessels. 

Vas-0-di-lat'or :  causing  dilation  or  relaxation  of  the  blood  vessels. 

Vas-o-mo'tor  :  regulating  the  tension  of  the  muscular  walls  of  the 
blood  vessels. 

Vein  (Lat.  vena)  :  one  of  the  tubes  carrying  blood  to  the  heart. 

Ve'na  ca'va  (Lat.,  hollow  vein)  :  one  of  the  great  veins  connected 
directly  with  the  heart. 

Ven-ti-la'tion  (Lat.  ventilare,  to  air,  ventilate)  :  the  process  of  repla- 
cing foul  or  vitiated  air  in  any  confined  space  with  pure  air. 

Ven'tral  (Lat.  venter,  belly)  :  toward  the  belly ;  opposed  to  dorsal. 

Ven'tri-cle  (Lat.  ventriculus,  diminutive  of  venter,  belly)  :  a  cavity,  as 
the  ventricles  of  the  heart  or  the  brain. 

Ver'te-bra  (Lat.,  a  bone  of  the  spine)  :  any  segment  of  the  backbone. 

Ver'te-brates  :  animals  having  a  backbone. 

Ves'ti-bule  (Lat.  vestibulum,  vestibule)  :  the  central  part  of  the  laby- 
rinth of  the  ear. 

Villus  (Lat.,  shaggy  hair)  :  one  of  the  minute  projections  covering 
the  valvulae  conniventes. 


394  GLOSSARY 

Vis'ce-ra  (Lat.,  plu.  of  viscus,  perhaps  akin  to  Eng.  viscid)  :  the  organs 
contained  in  the  abdomen. 

Vital  knot :  the  nervous  center  in  the  medulla  oblongata  which  pre- 
sides over  the  coordination  of  the  respiratory  movements.  If  the 
medulla  be  divided  below  this  center  respiration  ceases  and  death 
results. 

Vit're-ous  humor  (Lat.  vitreus,  of  glass)  :  the  jellylike  substance  fill- 
ing the  posterior  chamber  of  the  eyeball. 

Viv-i-sec'tion  (Lat.  vivus,  living,  and  sectio,  a  cutting)  :  dissection  of 
a  living  body. 

Vo'cal  cords  (Lat.  vox,  vocis,  voice) :  bands  of  elastic  tissue  in  the 
mucous  membrane  of  the  larynx  which  act  upon  the  air  like  the 
reeds  of  a  musical  instrument  to  produce  musical  sounds. 

Vo'mer  (Lat.,  a  plowshare) :  a  small  bone  forming  part  of  the  parti- 
tion between  the  nostrils. 

Yellow  spot :  an  area  about  one  twenty-fourth  of  an  inch  in  diameter 
in  the  retina  of  the  eye,  upon  which  the  most  definite  images  are 
formed. 


INDEX 


Abdomen,  163,  186,  221,  224. 

Abduceus  nerve,  291. 

Absorbents.  224. 

Absorption,  145,  202,  236,  237. 

Accelerator  nerves,  178,  299. 

Accommodation  of  eye,  113,  114,  122. 

Adam's  apple,  136. 

Adipose  tissue,  24. 

Afferent  nerves,  30,  86,  298. 

Air  cells,  183,  184. 

Air,  composition  of,  187. 

expired,  187. 

necessity  for  pure,  362-364. 

temperature  of,  for  breathing,  193, 
194. 
Albumin,  204,  205,  214. 
Alcohol,  as  food,  245,  246. 

as  poison,  24(>-250. 

effects  on  blood  circulation,   171, 
172,  180. 

effects  on  bodily  heat,  271,  272. 

effects  on  character,  328-332. 

effects  on  excretion,  264,  265. 

effects  on  eye,  120. 

effects  on  growth,  54. 

effects  on  muscular  action,  78. 

effects  on  nervous  system,  325-332. 

effects  on  respiration,  194. 

effects  on  taste  and  smell,  99. 

effects  on  vocal  organs,  144. 

properties  of,  244,  245. 
Alimentary  canal,  218-236. 

excretion  in,  263. 

peristaltic  movement  in,  67. 

relation  to  kidneys,  262. 
Alveolus,  183. 
Amoeba,  14, 16,  149. 
Ampulla,  128. 
Amylopsin,  253,  note  1. 
Anabolism,  202. 


Anatomy,  7. 

Animal  heat,  266,  267. 

Animals,  cells  of,  11. 

distinguished  from  plants,  13,  14. 
Ankle,  bones  of,  46. 
Antidotes  of  poisons,  355-359. 
Antiseptic  surgery,  340. 
Antitoxin,  338,  339. 
Anus,  227. 
Anvil  bone,  127. 
Aorta,  157,  161-163,  169. 
Appendices,  of  heart,  154. 
Appendicular  skeleton,  38,  45-49. 
Appendix,  vermiform,  226. 
Appetite,  control  of,  332-334. 
Aqueduct  of  Sylvius,  289. 
Aqueous  humor,  110. 
Arachnoid  membrane,  283. 
Areolar  tissue,  23,  59. 
Arm,  bones  of,  46. 
Arterial  blood,  174,  188, 197. 
Arteries,  158,  162-164. 

aorta,  157,  161-163,  169. 

blood  flow  in,  168. 

course  of  principal,  345,  34(5. 

function  of,  153,  164. 

injury  to,  168,  345,  3i6. 

muscular  action  of,  179,  180. 

pulmonary,  156,  164,  184. 

splenic,  163.  254. 

structure  of,  158,  159. 
Articular  cartilage,  51. 
Articular  processes,  anterior  and  pos- 
terior, 42. 
Articulations,  defined,  49. 
Arytenoid  cartilages,  136. 
Asphyxia,  relief  for,  347. 
Assimilation,  145,  202,  238. 
Astigmatism,  123. 
Atlas  vertebra,  43,  50. 


395 


396 


INDEX 


Atom,  defined,  9, 10. 
Auditory  area,  313. 
Auditory  cells,  132. 
Auditory  fatigue,  134,  135. 
Auditory  hairs,  132. 
Auditory  nerve,  128,  130,  291. 
Auditory  ossicles,  127. 
Auditory  word  center,  141. 
Auricle,  left,  155. 

right,  154. 
Autointoxication,  263,  2G4. 
Automatic  movement,  73. 
Axial  skeleton,  38-47. 
Axillary  artery,  162. 
Axis  cylinder  process,  32,  276. 
Axis  vertebra,  44,  50. 

Bacilli,  see  bacteria. 

Bacteria,  action  on  body,  336-338. 

function  of,  335,  336. 

in  decomposition,  243. 

in  intestines,  235. 
Ball  and  socket  joint,  50. 
Basal  ganglia,  287. 
Bathing,  public,  366. 
Belly  of  muscle,  61,  65. 
Biceps  muscle,  65. 
Bicuspid  valves,  157. 
Bicuspids,  219. 
Bile,  234,  237,  253,  338. 
Bile  duct,  231. 
Binocular  vision,  124. 
Bladder,  260. 

Blind  spot  of  eye,  109,  124. 
Blood,  absorption  in,  236. 

arterial,  174, 188,  197. 

as  tissue,  147. 

chemical  composition  of,  149. 

circulation  of,  145,  153-175. 

clotting  of,  149-152,  344,  345. 

effect  of  respiration  on,  187,  188. 

function  of,  26,  147. 

quantity  of,  in  body,  148. 

structure  of,  148. 

supplied  to  lungs,  184. 

velocity  of,  168. 

venous,  174,  197. 
Blood  corpuscles,  151. 

red,  26,  148-151,  188. 

white,  12,  16,  149,  151.  169-171,  255, 
338. 


Blood  pressure,  in  arteries  and  veins, 
168. 

in  brain,  179. 
Blood  vessels,  for  muscles,  61. 

in  bones,  52,  53. 

in  dermis,  85. 

injuries  to,  150,  345. 

nerves  for,  160,  179. 

structure  of,  174. 

supply  of,  159,  160. 

vascular  and  nervous  supply  of,  159, 
160, 179. 

see  arteries,  veins,  capillaries. 
Blushing,  168,  180. 
Bone  cells,  53. 
Bone  corpuscles,  26,  53. 
Bones,  articulations  of,  49. 

broken,  55. 

dissection  of,  57. 

function  of,  37. 

hygiene  of,  53-55. 

motion  of,  49,  50. 

number  of,  38. 

of  appendicular  skeleton,  45-47. 

of  axial  skeleton,  39-45. 

of  children,  53,  54. 

of  old  people,  55. 

structure  of,  25,  26,  50-52. 

table  of,  47,  48. 
Brachial  artery,  162. 
Brain,  blood  pressure  in,  179. 

dissection  of,  33,  295. 

membranes  of,  283. 

nerve  center,  239,  275. 

parts  of,  28,  284,  285. 

stimulus  for  perception,  91. 

ventricles  of,  289. 
Breastbone,  44,  45. 
Bright's  disease,  265. 
Broken  bones,  55. 
Bronchi,  182, 183. 
Bronchial  arteries,  163,  184. 
Bronchial  tubes,  183. 
Burns,  remedies  for,  349,  350. 

Caecum,  226. 
Canals  in  ear,  128,  133. 
Canines,  219. 
Capillaries,  action  of,  168. 

bleeding  from,  345. 

function  of,  150,  151, 153,  160. 


INDEX 


'397 


Capillaries,  lymph,  160. 

velocity  of  blood  in,  169. 
Carbohydrates,  203,  205,  236. 
Carbon,  in  food,  201,  204,  207. 
Carbon  dioxide,  181,  187-190,  257,  261 ; 

see  respiration. 
Carbonic  acid  gas,  see  carbon  dioxide. 
Cardiac  muscle,  158. 
Cardiac  nerves,  176-178. 
Cardiac  orifice  of  stomach,  222. 
Carotid  arteries,  162. 
Carpus,  46. 
Cartilage,  articular,  51. 

costal,  44,  45. 

forms  of,  24. 

function  of,  48. 

of  Santorini,  137. 

of  Weisberg,  1.37. 

permanent,  48. 

study  of,  56. 
Casein,  204,  205. 
Caseinogen,  216. 
Cells,  11. 

air,  183,  184. 

auditory,  132. 

bone,  53. 

forming  tissue,  19. 

motor,  72. 

muscle,  61,  G&. 

nerve,  32,  275. 

taste,  95. 
Cellulose,  205. 

Central  lobe  of  cerebrum,  285. 
Central  nervous    system,  27-30,  275, 

279-292,  .305-313. 
Centrum  of  vertebra,  42. 
Cerebellum,  composition  of,  287. 

function  of,  69,  70, 133,  306,  307. 

nervous  matter  in,  30. 
Cerebral  nerves,  see  cranial  nerves. 
Cerebro-spinal  fluid,  289. 
Cerebro-spiual  meninges,  284. 
Cerebro-spinal  nervous  system,  27-30, 

275,  279-292,  ;305-313. 
Cerebrum,  cortex  of,  30,  285,  311-313. 

functions  of,  .308-310. 

nervous  matter  in,  30. 

structure  of,  285-287. 
Cervical  vertebrae,  41, 
Character,  formation  of,  323-325. 
Cheek  bones,  40. 

macy's  phys. — 25 


Chemical  analysis,  9,  10. 

Chemical  element,  9,  10. 

Chest,  cavity  of,  45. 
muscles  of,  185,  186. 

Chiasma,  optic,  104. 

Chilblains,  treatment  for,  350. 

Choking,  treatment  for,  351. 

Chorda  tympani,  291. 

Choroid,  106. 

Chyle,  defined,  1.51. 

tubes  conveying,  153,  226,  237. 

Chyme,  231. 

Ciliary  muscles,  60,  111,  113,  114. 

Ciliary  nerves,  111. 

Ciliary  processes,  107,  114. 

Ciliated  epithelium,  91,  183. 

Circulation  of  blood,  1515-175. 

an  unconscious  nervous  operation, 

145. 
effects  of  alcohol  on,  180. 
general  or  systemic,  160-164. 
in  frog's  foot.  174. 
nervous  control  of,  176-180. 
portal,  160,  164,  165.. 
pulmonary,  160,  164. 

Circumvallate  papillae,  95. 

Clavicle,  45,  46. 

Cleanliness,  362. 

Clothing,  healthful,  268-271. 

Clotting  of  blood,  149-152,  344,  345. 

Coats  of  eye,  105,  106. 
I  Coccyx,  30,  42. 
I  Cochlea,  128,  129. 

Coeliac  axis,  163. 

Cold,  sensation  of,  88,  93. 
I  Colds,  cause  of,  337. 
'  Collar  bone,  46. 
I  Colon,  226. 

Color,  complementary,  125. 
i        production  of,  102. 
I  Color  blindness,  118,  125. 
\  Combustion,  see  oxidation. 
1  Commissure,  optic,  104. 
I  Conductivity  of  cells,  12. 

Cones  and  rods,  104,  108. 

Conjunctiva,  106. 

Connective  tissues,  21,  23,  24,  48,  147. 
i  Conscious  nervous  operations,  35-144. 
!  Consciousness,  310. 

Conservation  of  energy,  203. 
;  Consumption,  339-341. 


398 


INDEX 


Contractile  substance,  61. 

Contractility  of  cells.  12. 
Contraction  of  muscle,  (52-65,  SO. 
Convulsions,  relief  for,  353. 
Cooking,  principles  of.  209-213. 
Coordination  of  cells,  12. 
Coordination  of  muscular  movement. 

69,  70,  133,  306,  oO~. 
Coral,  rudiments  of  nervous  system  in, 

U. 
Corium.  82. 
Cornea,  105. 
Coronary  arteries.  162. 
Coronary  veins.  155.  161. 
Corpora   quadrigemina,   2S,  284,  287, 

307,  308. 
Corpora  striata,  287,  295. 
Corpus  callosum,  286. 
Corpuscles,  bone,  26,  53. 
Pacinian,  87. 

red  blood,  26,  148-151,  188. 
taste,  218. 
touch.  87,  88. 
white  blood,  12,  16,  18,  26,  149,  151, 

169-171,  255,  338. 
Correlation  of  forces,  203. 
Corrosive  poisons.  354.  355. 
Cortex,  of  cerebrum,  30,  285,  311-313. 

of  kidneys,  260. 
Corti,  organ  of,  130. 
Costal  cartilages,  44.  45. 
Cranial  boneS,  39.  40. 
Cranial  nerves.  28.  28it-295;  40,  95,  96, 

103,  104.  106.  108.  Ill,  112,  128, 

130,  141,  142,  176-178,  229,  232. 
Cranium,  39. 
Cricoid  cartilage,  136. 
Crura  cerebri.  28.  287,  307. 
Crystalline  lens,  109, 113, 114. 
Cuticle,  82,  83,  88,  92. 

Dead  muscle,  65,  66. 
Deafness,  143. 

Decussation  of  pyramids,  288. 
Deformity,  causes  of.  54,  55. 
Delirium  tremens,  326. 
Dendrites,  278. 
Dendrons.  278. 
Dentine,  220. 
Dermis,  82,  84,  85. 
Dialyzer,  175. 


Diaphragm,  185, 195. 
Diffusion  of  gases,  186. 
Digestion,  defined,  201,  202. 

experiments  in,  251-253. 
Digestive  apparatus,  218-236, 

dissection  of,  251. 
Dipsomania,  325,  326. 
Disease,  335. 

Dissection,  in  class  work,  15. 
Distillation,  244. 
Dorsal  vertebrje,  41. 
Drainage,  363. 

Drowning,  treatment  for,  347. 
Ductless  glands,  254-256. 
Ducts,  bile,  231. 

of  glands.  228. 

thoracic,  169. 
Dumbness,  143. 
Dura  mater,  283. 

Ear,  bones  of,  40. 

care  of,  134. 

dissection  of,  135. 

drum,  126,  127. 

external,  126. 

foreign  bodies  in,  352. 

internal,  127-131. 

middle,  127.  • 

muscular  fibers  of,  60. 

path  of  auditory  impression,  131- 
133. 
Efferent  nerves,  30,  86,  298,  299. 
Eggs,  as  food,  203,  204. 
Elements,  chemical,  9, 10. 

nervous.  275. 
Emulsion,  232,  237. 
Enamel  of  teeth,  220,  239,  240. 
End  bulbs,  88. 
End  organs,  for  hearing,  130. 

for  taste,  95. 

nervous,  292. 

of  olfactory  nerves,  98. 

of  vision,  104. 

tactile,  87,  88. 
End  plates,  62,  63,  292. 
Endocardium,  158. 
Endoskeleton,  37. 
Endothelium,  22. 
Energy,  conservation  of,  203. 

development  of,  21,  22. 

forms  of,  202,  203. 


INDEX 


399 


Energy,  from  foods,  207,  208. 

radiant,  102. 
Epidermis,  82,  83,  88,  92. 
Epigastric  plexus,  223. 
Epiglottis,  137. 
Epilepsy,  relief  for,  .353. 
Epithelium,  21-23,  82. 

ciliated,  91,  183. 
Equilibrium  of  body,  307. 
Esophageal  arteries,  163. 
Esophagus,  function  of,  137. 

muscular  fibei's  of,  60. 

structure  of,  221. 
Ether,  101,  102. 
Ethmoid  bone,  40. 
Eustachian  tube,  127. 
Excretion,  function  of,  201,  2.38. 

influence  of  alcohol  on,  264,  265. 

organs  of,  82,  257-265. 
Exercise,  value  of,  74-77. 
Exoskeleton,  .37. 
Expiration,  184,  185. 

center  of,  199. 
Eye,  101-125. 

as  optical  instrument,  112,  113,  121, 
122. 

care  of,  119,  120. 

coats  of,  105,  106. 

defects  of  vision,  116-118. 

dissection  of,  120,  121. 

duration  of  sight  sensation,  116. 

fatigue  of  retina,  116. 

foreign  bodies  in,  .351,  352. 

muscles  of,  110,  111. 

parts  of,  105-109. 

structure  of,  103-105. 
Eyeball,  104,  105. 
Eyebrows,  112. 
Eyelids,  60,  111. 

Facial  nerve,  291. 

Facial  skeleton,  40. 

Faces,  236. 

Fainting,  relief  for,  178,  352. 

Farsightedness,  124. 

Fatigue,  auditory,  134,  135. 

of  muscle,  64,  80. 

of  nerve  cells,  317. 

of  retina,  116,  125. 

of  smell,  98, 100. 
Fats,  203,  205,  215,  232. 


Fatty  degeneration,  248,  265. 
Femoral  ai'tery,  163. 
Femur,  46. 
Fenestra  ovalis,  127. 
Fenestra  rotunda,  127. 
Fermentation,  of  organic  tissue,  243. 

vinous,  243,  244. 
Ferments,  action  of,  2;3(J-232,  2:^4. 

fibrin,  150. 
Fibers,  muscle,  60,  61,  66. 

nerve,  see  nerves. 
Fibrin,  1.50,  152,  205. 
Fibrin  ferment,  1.50. 
Fibrinogen,  150. 
Fibrocartilage,  24,  43. 
Fibrous  tissue,  24. 
Fibula,  46. 
Filiform  papillae,  95. 
Fingers,  bones  in,  46. 
Fissures  of  cerebrum,  285,  286. 
Flavors,  96. 
Floating  ribs,  45. 
Focus  of  rays  of  light,  103. 
Follicles,  hair,  83,  2.58. 
Food,  201-217. 

alcohol  as,  245. 

classification  of,  204. 

cooking  of,  209-213. 

defined,  201. 

effect  of  gastric  juice  on,  231. 

forchildren,  53,54,  240. 

mastication  of,  241. 

necessity  for,  147. 

nitrogenous,  205,  208. 

nonnitrogenous,  205,  208. 

pure,  364. 

quantity  of,  242,  243. 

undigested,  209. 

values  of,  207,  208. 

variety  in  diet,  208,  209,  242. 
Food  accessories,  204,  206. 
Food  elements,  20.3-206. 
Foramen  magnum,  40, 279. 
Foramen  of  Munro,  295. 
Forces,  correlation  of,  203. 
Fornix,  295. 

Framework  of  body,  see  skeleton. 
Frontal  bone,  .39. 
Frontal  lobe  of  cerebrum,  285. 
Frost  bites,  treatment  of,  350. 
Fungiform  papillae,  95. 


400 


INDEX 


Gall  bladder,  2U. 
Ganglia,  basal,  287. 

composition  of,  32. 

defined,  275,  278. 

of  sympathetic  nervous  system,  30, 
292-295. 

spinal,  29. 
Ganglionic  nervous  system,  27,  30,  275, 

292-295,  304,  305. 
Garbage,  disposal  of,  366,  367. 
Gastric  artery,  163. 
Gastric  juice,  230,  252,  264. 
General  or  systemic  circulation,  160- 

164. 
Germs,  see  bacteria. 
Glands,  ductless,  254-256. 

lachrymal,  112. 

lymphatic,  169,  170. 

of  olfactory  membrane,  97. 

oil,  85. 

salivary,  228,  229. 

sebaceous,  258. 

structure  of,  227,  228. 

sweat,  85,  95,  258, 

wax,  127. 
Globulin,  205. 
Glomeruli,  260. 

Glossopharyngeal  nerve,  95,  229,  291. 
Glottis,  137,  138. 
Glucose,  235. 
Gluten,  205,216. 
Glycerin,  232. 
Glycogen,  2.34. 
Goiter,  255. 
Gray  nervous  matter,  30,  32,  275 ;  see 

nervous  system. 
Gristle,  see  cartilage. 

Habit,  302,  321-324. 

Hair,  as  organ  of  touch,  92. 

function  of,  84. 

structure  of,  83. 
Hair  cells  of  ear,  131. 
Hair  follicles,  83,  258. 
Hammer  bone,  40,  127. 
Hand,  bones  of,  4<i. 
Hard  palate,  40. 
Haversian  canals,  25,  .52. 
Hearing,  sense  of,  126-135. 
Heart,  action  of,  in  circulation,  166 
167. 


Heart,  dissection  of,  173. 

effects  of  stimulants  on,  171, 172. 
muscles  of,  60. 
nerves  of,  176-178. 
sounds  of,  167. 
structure  of,  153-158. 
Heat,  of  body,  266-272. 
sensation  of,  88,  93. 
Hemoglobin,  148,  188. 
Hepatic  artery,  163,  164. 
Hepatic  cells,  233. 
Hepatic  veins,  165. 
Heredity,  324-327. 
Hinge  joint,  50. 
Hip  bone,  46. 
Hippocampus,  295. 
Horns,  anterior  and  posterior,  of  spinal 

cord,  280. 
Humerus,  46. 
Humor,  aqueous,  110. 

vitreous,  108,  110. 
Hunger,  sensation  of,  86,  238,  239. 
Hyaline  cartilage,  24. 
Hydrochloric  acid,  230,  264. 
Hydrogen  in  food,  201,  204,  205. 
Hygiene,  7. 

of  bones  and  joints,  53-56. 

of  circulation,  171. 

of  clothing,  2H8-271. 

of  digestion,  239-243. 

of  ear,  134. 

of  exercise,  74-77. 

of  eye,  119,  120. 

of  food,  207-21.3. 

of  muscles,  73-76. 

of  nervous  system,  314-334. 

of  respiration,  192,  193. 

of  vocal  apparatus,  143,  144. 

public,  360-367. 
Hyoid  bone,  40,  137. 
Hypogastric  plexus,  223. 
Hypoglossal  nerve,  292. 
Hysterics,  treatment  for,  353. 

Ileocsecal  valve,  226. 
Iliac  arteries,  162,  163. 
Images,  formed  by  lenses,  103. 

inverted,  in  eye,  114,  121. 
Immunes,  339. 
Incisors,  218. 
Incus,  40, 127. 


INDEX 


401 


Inhibitory  nerves,  178,  291>. 

Innomiuate  artery,  162. 

Insomnia,  319. 

Inspiration,  184,  185,  200. 

Instability  of  protoplasm,  12,  1(3,  18. 

Insula,  28.-).  2S6. 

Intercellular  substance,  2o,  24,  48. 

Intercostal  arteries,  163. 

Intestinal  juice,  235. 

Intestines,  action  of  alcohol  on,  247. 

large,  226,  235,  236. 

peristaltic  movement  of,  235. 

small,  223,  224,  231,  235. 
Intraceutral  nerves,  299. 
Intrinsic  nerves,  of  heart,  177. 
Invertebrates,  exoskeleton  of,  37. 
Inverted  images,  114,  121. 
Involuntary  muscles,  60,  m,  67,  80,  81, 

158. 
Iris,  106, 107,  114. 

Irritability  of  protoplasm,  12,  14,  16, 
18. 

of  tissues,  21. 
Irritant  poisons,  354,  355. 
Island  of  Reil,  285,  286. 

Jaw  bones,  40. 

Joint,  function  of,  49,  50, 

injuries  to,  55,  5(). 

study  of,  57. 
Jugular  vein,  169. 

Katabolism,  202,  263. 
Kidneys,  257,  260-265. 
Kneepan,  46. 

Labyrinth  of  ear,  127-131. 
Lachrymal  bones,  40. 
Lachrymal  gland,  112. 
Lacteals,  151,  153,  170,  226,  237. 
Lacunse,25,  53. 
Lamellae,  52. 

Larynx,  nervous  mechanism  of,  141, 
142. 

structure  of,  13(i,  137. 

study  of,  144. 
Lens,  crystalline,  109,  113,  114. 

image  formed  by,  103. 
Levers,  in  human  body,  67-69. 
Ligaments,  function  of,  38,  48. 

study  of.  81. 


1  Ligament,  transverse,  44. 
I  Limbs,  bones  of,  46,  47. 
!  Liver,  232-234. 

blood  circulation  in,  KU,  165. 
effects  of  alcohol  on,  248. 
Lobes  of  cerebrum,  9<),  285. 
I  Lobes,  optic,  28,  284,  287,  307,  308. 
Locomotion,  organs  of,  59. 
Longsightedness,  117. 
Lumbar  vertebrae,  41. 
Lungs,  capacity  of,  186. 
excretory  organs,  257. 
structure  of,  184. 
see  respiration. 
Lymph,  circulation  of,  169. 

function  of,  23,  151. 
Lymph  capillaries,  169. 
Lymph  vascular  system,  153. 
Lymphatic  duct,  170. 
Lymphatic  glands,  170. 
Lymphatic  vessels,  151, 153,  237. 

Malar  bones,  40. 
Malleus,  40,  127. 
Marrow,  red,  52,  148. 

yellow,  51. 
Master  tissues,  21. 
Mastication,  218,  241. 
Matter,  intercellular,  23,  24,  48. 

living  and  lifeless,  9. 

nervous,  30,  32,  275;  see  nervous 
system. 
Maxillary  bones,  40. 
Meatus,  external,  126. 
Medulla  oblongata,  28,  285. 

reflex  center,  301,  306. 

structure  of,  288,  289. 
Medullary  cavity,  51. 
Medullary  portion  of  kidneys,  260. 
Medullary  sheath,  32,  33,  277. 
Medullated  nerve  fiber,  33. 
Membrane,  mucous,  see  mucous  mem- 
brane. 
Membranes,  of  brain  and  spinal  cord, 
283. 

of  tympanum,  126,  127. 

sjiiovial,  50. 
Membranous  labyrinth,  128. 
Memory,  310. 
Meninges,  284. 
Mesenteric  arteries,  163. 


402 


INDEX 


Mesentery,  224. 
Metabolism,  202. 
Metacarpus,  4(>. 
Metatarsals,  46. 
Microbes,  see  bacteria. 
Milk,  as  food,  203,  204,  216. 
Milk  teeth,  218. 
Mitral  valves,  157. 
Molars,  219. 
Molecule,  9,  10. 
Motion,  in  animals,  38. 

of  bones,  49. 

organs  of,  59. 

production  of,  30,  35,  44. 
Motor  areas,  311,  312. 
Motor  cells,  72. 
Motor  center,  141. 
Motor  nerves,  28,  30,  86,  299. 
Mouth,  218. 
Movement,  mechanism  of,  67-69. 

of  involuntary  muscles,  66,  67. 

reflex,  72,  73. 

voluntary,  71,  72. 
Mucous  membrane,  of  ear,  127. 

of  eye,  106. 

of  nose,  96,  97,  337. 

of  small  intestine,  224. 

of  stomach,  221. 

of  tongue,  94. 

of  trachea,  183. 

structure  of,  84. 
Mucus,  84. 
Muscle  waste,  71. 
Muscles,  cardiac,  158. 

changes  under  stimulus,  63,  64. 

classification,  60. 

composition  of,  59. 

contraction  of,  62-65. 

coordination    of    muscular    move- 
ments, 69,  70,  133,  306,  .307. 

dead,  65,  66. 

effects  of  stimulants  on,  78. 

fatigue  of,  70. 

function  of,  37,  .38. 

hygiene  of,  73,  76. 

involuntary,  60,  66,  67,  81. 

nerve  endings  in,  61. 

nerves  causing  contraction  of,  28. 

nervous  stimulus  of,  21 . 

of  blood  vessels,  179. 

of  frog,  17,  18. 


Muscles,  papillary,  157. 

plain,  see  involuntary. 

properties  of  protoplasm  in,  17,  18. 

proteids  in,  217. 

reflex  and  automatic  movements, 
71-73. 

relaxation,  65,  80. 

skeletal,  see  voluntary. 

study  of,  79-81. 

voluntary,  60,  61,  72,  73,  81. 
Muscular  fiber,  of  intestines,  224. 

of  stomach,  221,  222. 

plain  or  unstriped,  60,  66,  81, 

striated  or  striped,  60,  63,  81, 158. 
Muscular  movement,  coordination  of, 

69,  70,  133,  .306,  307. 
Muscular  power,  64,  65. 
Muscular  sense,  73,  86,  88,  89,  93. 
Muscular  system,  59-81. 
Muscular  tissues,  20,  21. 
Musical  sounds,  140. 
Myosin,  205,  217. 
Myosinogen,  217. 

Nails,  function  of,  84. 

structure  of,  84. 
Narcotics,  effects  of,  79,  332,354;  see 

alcohol,  tobacco. 
Nasal  bones,  40. 
Nearsightedness,  123. 
Nerve  cells,  fatigue  of,  32,  275,  317. 
Nerve  center,  30,  2.39,  275,  300. 
Nerve  endings,  in  muscle,  80. 
Nerve  fiber,  30,  .32-M,  276,  277. 
Nerves,  afferent,  30,  86, 298. 

cerebral,  see  cranial. 

controlling  circulation,  176-180. 

controlling  heat  production,  268. 

controlling  respiratory  apparatus, 
i  198-200. 

controlling  sweat  glands,  258,  259. 

cranial,  28,  289-295 ;  40,  95,  96,  103, 
104,  106,  108,  111,  112,  128,  130, 

.      141,  142,  176-178,  229,  232. 

efferent,  30,  86,  298,  299. 

end  organs  of,  61,  292. 

for  muscle,  61. 

function  of,  298. 

motor,  28,  .30,  86,  298,  2f)9. 

of  blood  vessels,  179. 

of  general  sensibility,  298. 


INDEX 


403 


Nerves,  of  heart,  176, 177. 

of  skin,  87. 

of  small  intestines,  224. 

of  stomach,  223. 

plexuses,  30,  (30,  87,  223,  224,  261, 
283,  295. 

respiratory,  198. 

sensory,  28,  30,  86,  298. 

spinal,  29,  72,  86,  87,  281-283. 

structure  of.  277,  278. 
Nervous  discharge,  2it9. 
Nervous  disorders,  314,  316,  320,  321, 

325-327. 
Nervous  elements,  275. 
Nervous  impulse,  passage  of,  22,  279. 
Nervous  operations,  conscious,  35-145. 

unconscious,  145-272. 
Nervous  prostration,  316. 
Nervous  system,  anatomical  descrip- 
tion, 275-296. 

cerehro-spinal  or  central,  27-30, 275, 
278,  305-313. 

controls  muscular  action,  70. 

functions  of,  22,  27,  35,  77,  297-313. 

habit  as  connected  with,  302,  321- 
324. 

hygiene  of,  314-334. 

influence  of  alcohol  on,  325-332. 

nutrition  of,  314-317. 

sympathetic  or  ganglionic,  27,  30, 
275,  292-295,  304,  305. 

vasomotor,  179,  ISO. 
Nervous  tissues,  20,  21,  30,  32,  275. 
Nervousness,  314. 
Neural  arch,  of  vertebra,  42. 
Neural  ring,  of  vertebra,  42. 
Neuraxon,  276,  278. 
Neurilemma,  32,  33,  61,  277,  278. 
Neurog;lia,  278. 
Nicotine,  effects  of,  332. 
Nitrogen,  in  air,  187. 

in  food.  201,  204-208,  261. 
Nodes,  33. 
Noise.  141. 

Noumedullated  nerve  tibers,  33,  277. 
Nounitrogeuous  food,  205,  208. 
Normal  salt  solution,  17. 
Nose,  bleeding  of,  .>4(i,  347. 

foreign  bodies  in,  352. 
Nucleus  of  cell,  11. 
Nutrition,  236-253. 


Nutrition,  defined,  201,  202. 
function  of,  11,  12. 
how  effected,  145. 
of  nervous  system,  314-317- 
organs  for,  59. 

Oblique  muscles,  110,  111. 

Occipital  bone,  40. 

Occipital  lobe,  285. 

Occipito-parietal  fissure,  286. 

Oculomotor  nerve,  104,  290. 

Odontoid  process,  44. 

Odors,  97. 

Oil  glands,  85. 

Olfactory  bulbs,  96,  286,  287. 

Olfactory  lobes,  9(3. 

Olfactory  nerves,  40,  9t)-98,  290. 

Olfactory  tract,  286. 

Omentum,  great,  221. 

Opium,  effects  of,  332. 

Optic  chiasma,  104. 

Optic  commissure,  104. 

Optic  lobes,  28,  284,  287,  307,  308. 

Optic  nerve,  103-106,  108,  290. 

Optic  thalami,  28,  284,  287,  ;308. 

Optic  tract,  105. 

Orbit  of  eye,  105. 

Organic  matter,  decomposition  of,  243. 

Organism,  defined,  20. 

Organs,  defined,  20. 

of  Corti,  130,  131. 

tissues  forming,  20. 
Os  innominatum,  46. 
Osmosis,  160,  175. 
Ossicles,  auditory,  127. 
Ossification,  process  of,  26. 
Otoliths,  132. 
Oval  window,  of  ear,  127. 
Overwork,  320,  321. 
Oxidation,  205-209,  227,  257,  267. 
Oxygen,  147, 149,  201-209,  227,  257, 267 ; 

see  respii'ation. 
Oxyhemoglobin,  188. 

Pacinian  corpuscles,  87. 
Pain,  sensation  of,  86,  89,  90. 
Palate,  hard,  40,  218. 

soft,  218. 
Palate  bones,  40. 
Palmar  arch,  162,  ]64. 
Pancreas,  231. 


404 


INDEX 


Pancreatic  juice,  231,  237,  253. 
Papillfe,  of  hair,  83. 

of  mouth,  218. 

of  palate,  94. 

of  skin,  85. 

of  tongue,  94,  95. 
Papillary  muscles,  157. 
Parietal  bones,  39. 
Parietal  lobe,  285. 
Parotid  glands,  228. 
Patella,  46. 

Pectoral  girdle,  37,  45,  46. 
Peduncles,  of  cerebellum,  287,  296. 

of  cerebrum,  28,  287,  307. 
Pelvic  arch,  41. 
Pelvic  girdle,  37,  45,  46. 
Pepsin,  230. 
Perception,  91,  310. 
Pericardial  arteries,  163. 
Pericardium,  153. 
Perimysium,  59. 
Perineurium,  278. 
Periosteum,  51,  52,  220. 
Peristaltic  movement,  66,  67,  223,  235, 

302. 
Peritoneum,  221,  224. 
Permanent  cartilage,  48. 
Peroneal  artery,  163. 
Perspiration,  258,  259. 
Phalanges,  46. 
Pharynx,  function  of,  220,  221. 

muscular  fibers  of,  60. 

position  of,  137. 
Phrenic  artery,  163. 
Phrenic  nerve,  198. 
Physiology,  7. 
Pia  mater,  283. 
Pigment,  of  eye,  106,  107. 

of  skin,  83,  84. 
Pinna,  126. 
Pitch,  141. 
Pivot  joint,  50. 
Plain  muscle,  60,  66,  67,  81. 
Plants,  cells  of,  11. 

distinguished  from  animals,  13, 14, 

movements  of  protoplasm  in,  17, 

proteids  manufactured  by,  204. 
Plasma,  26,  148,  338. 
Pleura,  184. 

Plexus,  epigastric,  223,  295. 
function  of,  87,  283. 


Plexus,  hypogastric,  223. 

of  plain  muscle  fiber,  66. 

of  sympathetic  system,  30. 

renal,  261. 

solar,  223,  295. 
Pneumogastric    nerve,  141,  176,  239, 

292. 
Poisons,  and  their  antidotes,  353,  359. 

in  system,  263,  264. 
Pons  Varolii,  28,  284,  288,  306. 
Popliteal  artery,  163. 
Portal  circulation,  160, 164, 165. 
Portal  vein,  164, 165. 
Premolars,  219. 
Pressure  sense,  93. 
Primitive  sheath,  61. 
Process,  axis  cylinder,  32, 

of  nerve  cells,  32,  275,  276. 

spinous,  42. 
Proteids,  203-205. 

absorption  of,  2.36. 

action  of  gastric  juice  on,  230,  231. 

action  of  pancreatic  juice  on,  231, 
232. 

defined,  11. 

tests  for,  214. 
Protoplasm,  defined,  10, 11.     , 

in  muscle,  17,  18. 

in  plants,  17. 

properties  of,  12,  14,  16, 18. 
Pseudopodia,  16. 
Ptyalin,  229,  230. 
Pulmonary  artery,  156, 164,  184. 
Pulmonary  circulation ,  160,  164. 
Pulmonary  veins,  155,  164. 
Pulse,  166. 

Pupil  of  eye,  106, 107. 
Putrefaction,  243. 
Pylorus,  222. 
Pyramids,  in  kidneys,  260. 

in  medulla  oblongata,  288. 

Radial  artery,  162. 

Radiant  energy,  102. 

Radius,  46,  50. 

Rectum,  226. 

Rectus  muscles,  110, 

Red  blood  corpuscles,  26, 148-151,  188. 

Reflex  action,  72,  73, 178,  200,  300-304. 

Refraction,  102,  103, 121, 

Relaxation  of  muscles,  65,  80. 


INDEX 


405 


Renal  artery.  163. 
Kenal  plexus,  2(il. 
Rennet.  2^).  252. 
Reunin.  2:*).  253. 
Reproduction,  12. 
Resonating  cavities,  139. 
Respiration.  181-2tX). 

artificial.  ;^S,  349. 

effects  of  alcohol  and  tobacco  on, 

muscular  action  in,  60,  185,  186. 

organs  of.  181.  li^,  195. 
Respiratory  apparatus,  nervous  control 

of,  198-200. 
Retina,  103.  100-108. 

fatigue  of,  116,  125. 
Rhythmic  movements  of  involuntary 

muscles,  tiO,  67. 
Ribs,  action  in  respiration,  43, 185, 186, 
195.  19(i. 

attachment  to  spinal  column,  41. 

floating.  -4.5. 

structui'e  of,  44,  45. 
Rickets,  54. 
Rigor  mortis,  65,  80. 
Rods  and  cones  of  eye.  104.  108. 
Rods  of  Corti.  130,  131. 
Round  window,  of  ear,  127. 

Sacciile.  128. 

Sacral  arteries,  162. 

Sacrum,  41. 

Saint  Vitus's  dance,  causes  of,  77. 

Saliva,  action  of.  229. 

destroys  bacteria,  337. 

study  of.  251.  252. 
Salivary  glands,  228.  229,  241. 
Salts,  as  food  elements,  203,  206.  261. 

in  gastric  juice.  230. 

skin  excretes.  257,  258. 
Sanitation,  general,  3(,iO-367. 
Santorini,  cartilages  of,  137. 
Saponification.  232,  237. 
Sarcolemma,  59,  61. 
Scala  tympaui,  129. 
Scala  vestibuli,  129. 
Scalds,  treatment  for.  349. 
Scapula.  45. 

Sclerotic  coat  of  eye,  106. 
Sea  anemone,  rudiments  of  nerve  sys- 
tem in.  14. 


Sebaceous  glands,  258. 
Secreting  cells.  2i>2. 
Secretion,  227-235. 
Secretory  nerves,  299. 
Self-control,  303. 
Semicircular  canals.  128,  133. 
Semilunar  valves,  157, 159. 
Sensation,  conditions  essential  for,  85. 

general,  85. 

production  of,  35. 
Sense,  muscular,  73,  86,  88,  89. 

of  hearing.  14,  86,  126-135. 

of  sight,  14,  86,  101-125. 

of  smell,  14,  86,  96-99. 

of  taste,  14,  86,  94-96. 

of  touch,  14,  86-91. 
Sensory  areas,  312. 
Sensory  nerves,  28,  :¥),  86,  298. 
Serrated  sutures,  49. 
Serum,  150. 
Serum  albumin,  217. 
Sewage,  disposal  of,  366,  367. 
Sheath,  primitive.  61. 

medullary,  32,  33,  277. 
Shortsightedness,  117. 
Shoulder  blade,  45. 
Sight  sensation,  duration  of,  116, 125 
Sight,  sense  of,  14,  86, 101-125. 
Sinus,  265. 

Skeletal  muscles,  60,  61,  72,  73,  81. 
Skeleton,  38-57. 

appendicular,  45-48. 

axial,  47. 

facial,  40. 

study  of,  56,  57. 
Skin,  function  of,  82,  257-259. 

organ  of  touch,  86. 

regulator  of  heat  loss,  267. 

relation  to  kidnej^s,  262. 

structure  of,  82,  258. 

study  of.  91,  92. 
Skull,  parts  of,  39,  49. 
Sleep,  317-320. 
Smell,  area  for,  313. 

combination  with  taste,  100. 

sense  of,  14,  86,  96-99. 
Snifling,  97. 
Solar  p^lexus,  223,  295. 
I  Sound,  conduction  of.  40. 
j        direction  of,  133-135. 
I       production  of,  139. 


406 


INDEX 


Spectrum,  102. 
Speech,  141.  312. 
Sphenoid  hone,  40. 
Sphincter  muscle,  223. 
Spinal  accessory  nerve,  176, 177,  292. 
Spinal  hulb,  see  medulla  oMongata. 
Spinal  column,  40-44. 
Spinal  cord,  center  reflex  action,  73, 
302,  303. 

function  of,  300. 

membranes  of,  283. 

nerve  center,  275. 

structure  of,  29,  32,  279,  280. 

study  of,  34. 
Spinal  ganglion,  29,  282. 
Spinal  nerves,  29,  72,  86,  87,  281-283. 
Spinous  process,  42. 
Spleen,  149,  254,  255. 
Splenic  artery,  163,  254. 
Splenic  vein,  255. 
Sprain,  treatment  of,  56. 
Squamous  epithelium,  91. 
Squinting,  causes  of,  117,  118, 
Stammering,  causes  of,  141. 
Stapes,  40,  127. 
Starch,  205,  214. 
Sterilizing,  340. 
Sternum,  44,  45. 
Stimulus,  in  plants  and  animals,  14. 

nervous,  21. 

of  muscle,  21,  62-64. 

results  of,  309,  310. 
Stirrup  hone,  40,  127. 
Stomach,  absorbents  in,  236. 

action  of  alcohol  in,  247. 

action  of  gastric  juice  in,  230,  231. 

structure  of,  221-223. 
Striped    (striated)   muscle  fibers,  60, 

63,  81,  158.  . 
Stroma,  148. 
Subclavian  arteries,  162. 
Sublingual  glands,  228. 
Submaxillary  glands,  228. 
Suffocation,  treatment  for,  347. 
Sugar,  205. 

conversion  of  starch  into,  229,  232. 

liver  stores  up,  234. 

test  for,  215. 
Sunstroke,  treatment  for,  350,  351. 
Suprarenal  capsules,  256. 
Suspensory  ligament,  109. 


Sutures,  37,  49. 
Sweat,  258,  259. 
Sweat  glands,  85,  92,  258. 
Sylvian  fissure,  286. 
Sympathetic  nervous  system,  compo- 
sition of,  30,  292-295. 

functions  of,  27,  304,  305. 

nerves  from,  278. 

study  of,  34. 
Synovial  fluid,  56. 
Synovial  membrane,  50, 
System,  20. 
Systemic  circulation,  160-164. 

Tactile  end  organs,  87,  88. 
Tactile  sensations,  area  for,  313, 
Tarsal  bones,  46. 
Taste,  area  for,  313. 

combination  with  smell,  100. 

sense  of,  14,  86,  94-96. 
Taste  buds,  95,  96. 
Taste  cells,  95. 
Taste  corpuscles,  218. 
Tear  ducts,  40. 
Tears,  formation  of,  112. 
Teeth,  218-220. 

care  of,  240,  241. 

enamel  of,  239,  240. 
Temperature,  of  air  for  breathing,  193, 
194. 

of  body,  82,  266-268. 

sensation  of,  86,  93. 
Temporal  bones,  39. 
Temporal  lobe,  285. 
Tendinous  cords,  157. 
Tendons,  function  of,  48. 

study  of,  81. 
Tetanus,  63. 
Thermic  fever,  350,  351. 
Thigh  bone,  46. 
Thirst,  sensation  of,  86,  238. 
Thoracic  duct,  169,  237. 
Thoracic  vertebrae,  41. 
Thorax,  arteries  in,  162,  163. 

contraction  of  muscles  of,  45, 185. 

in  breathing,  184,  185. 
Thymus  gland,  256. 
Thyroid  cartilage,  136,  137. 
Thyroid  gland,  255,  256. 
Tibia,  46. 
Tibial  artery,  163. 


INDEX 


407 


Tissue-forming  foods,  204. 
Tissues,  classilication  of,  20-26. 

connective,  48. 

differentiation  of,  19,  20. 

nervous,  275. 

organic,  243. 
Tobacco,  diseases  from  use  of,  332. 

effects  on  blood  circulation,  172. 

effects  on  growth,  54. 

effects  on  muscular  actions,  79. 

effects  on  respiration,  194. 

effects  on  vocal  organs,  144. 
Toes,  bones  of,  46. 
Tongue,  function  of,  218. 

structure  of,  94,  95. 

study  of,  99. 
Tonsils,  220. 
Touch,  Aristotle's  experiment  for,  92. 

discrimination  in,  88,  92. 

path  of  touch  impression,  90,  91. 

sense  of,  14,  82,  86-91. 
Touch  corpuscles,  87,  88. 
Toxins,  337,  338. 
Trachea,  182. 
Transverse  ligament,  44. 
Transverse  processes,  42. 
"Tree    of    life,"    cerebellum    called, 

288. 
Triceps  muscle,  65. 
Tricuspid  valves,  156,  157. 
Trigeminal  nerve,  95,  104,  112,  291. 
Trochlear  nerve,  291. 
Trommer's  test  for  sugar,  215. 
Trophic  nerves,  299. 
Trunk  of  body,  37. 
Trypsin,  253,  note  1. 
Tuberculin,  340. 
Tuberculosis,  339-341. 
Turbinate  bones,  40. 
Tympanic  passage,  129. 
Tympanum,  126,  127. 

Ulna,  46,  50. 

Ulnar  artery,  162. 

Unconscious  nervous  operations,  145- 

272. 
Undigested  food,  209. 
Urea,  207,  234,  257,  261,  262. 
Ureter,  260. 
Urine,  260. 
Utricle,  128. 


Vaccination,  339. 
Vagus  nerve,  141,  176,  239,  292. 
Valve,  ileocffical,  226. 
Valves,  in  veins,  159,  174. 

of  heart,  156,  157,  159,  166,  167. 

of  lympathic  vessels,  237. 
Valvulae  conniventes,  224,  225. 
Vascular  system,  153. 
Vasoconstrictor  nerves,  179,  304. 
Vasodilator  nerves,  179,  304. 
Vasomotor  nervous  system,  179,  180. 
Veins,  continuous  blood  flow  in,  168. 

function  of,  153. 

in  portal  circulation,  164,  165. 

injury- to,  168,  345,  346. 

muscular  action  of,  179. 

principal,  164. 

pulmonary,  155,  164. 

splenic,  255. 

structure  of,  159. 

valves  in,  174. 
Vena  cava,  154,  155,  164,  169. 
Venous  blood,  188, 197. 
Ventilation,  190-192. 
Ventricles,  of  brain,  289. 

of  heart,  154,  156,  157. 

of  throat,  138. 
Vermiform  appendix,  226. 
Vertebrae,  41-44. 
Vertebral  column,  40-44. 
Vertebrate  skeleton,  37-48. 
Vestibular  passage,  129. 
Vestibule  of  ear,  128,  133. 
Villi,  225. 
Vision,  area  for,  313. 

binocular,  124. 

defects  of,  116-118. 

defined,  101. 

nervous  apparatus  for,  103,  104. 
Visual  center,  103. 
Vital  knot,  305. 
Vital  processes,  145. 
Vitreous  humor,  108, 110. 
Vivisection,  15. 
Vocal  apparatus,  136-145. 
Vocal  cords,  137.  138. 
Vocalization,  139. 
Voice,  care  of,  143,  144. 
Volition,  310. 
Voluntary  action,  300-303. 
Voluntary  movement,  71,  72. 


408 


INDEX 


Voluntary  muscles,  60,  61,  63, 
Vomer,  40. 


81. 


Waste  products,  71,  82,  181,  190,  207, 

261 ;  see  excretion. 
Water,  excreted  by  the  kidneys,  257, 
261. 
excreted  by  the  skin,  257-259. 
in  gastric  juice,  230. 
necessity  for  pure,  364-366. 
uses  in  nutrition,  206. 
Wax  glands,  127. 
Weisberg,  cartilages  of,  137. 
Whispering,  139. 

White  blood  corpuscles,  described,  149, 
151. 
function  of,  338. 


White  blood  corpuscles,  in  lymphatic 
system,  169-171. 

properties  of,  12. 

spleen  manufactures,  255. 

study  of,  16. 
White  fibrous  tissue,  24. 
White  light,  production  of,  102, 
White  nervous  matter,  30,  32,  275 ;  see 

nervous  system. 
White  substance  of  Schwann,  277. 
Wisdom  teeth,  219. 
Work,  healthfulness  of,  76. 
Wounds,  surface,  344. 
Wrist,  bones  of,  46. 

Yeast,  24S-245. 
Yellow  spot  of  eye,  109. 


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